diff --git a/bindings/node/index.js b/bindings/node/index.js
index 26f1ceae..aa8561ca 100644
--- a/bindings/node/index.js
+++ b/bindings/node/index.js
@@ -310,7 +310,7 @@ if (!nativeBinding) {
   throw new Error(`Failed to load native binding`)
 }
 
-const { version, SMA, EMA, WMA, RSI, DEMA, TEMA, HMA, ROC, TRIX, SMMA, TRIMA, ZLEMA, T3, VWMA, MOM, CMO, TSI, PMO, StochRSI, UltimateOscillator, PPO, DPO, Coppock, AroonOscillator, Vortex, MassIndex, MACD, BollingerBands, ATR, Stochastic, OBV, ADX, CCI, WilliamsR, MFI, PSAR, Keltner, Donchian, VWAP, AwesomeOscillator, Aroon, KAMA } = nativeBinding
+const { version, SMA, EMA, WMA, RSI, DEMA, TEMA, HMA, ROC, TRIX, SMMA, TRIMA, ZLEMA, T3, VWMA, MOM, CMO, TSI, PMO, StochRSI, UltimateOscillator, PPO, DPO, Coppock, AroonOscillator, Vortex, MassIndex, NATR, StdDev, UlcerIndex, HistoricalVolatility, MACD, BollingerBands, ATR, Stochastic, OBV, ADX, CCI, WilliamsR, MFI, PSAR, Keltner, Donchian, VWAP, AwesomeOscillator, Aroon, KAMA } = nativeBinding
 
 module.exports.version = version
 module.exports.SMA = SMA
@@ -339,6 +339,10 @@ module.exports.Coppock = Coppock
 module.exports.AroonOscillator = AroonOscillator
 module.exports.Vortex = Vortex
 module.exports.MassIndex = MassIndex
+module.exports.NATR = NATR
+module.exports.StdDev = StdDev
+module.exports.UlcerIndex = UlcerIndex
+module.exports.HistoricalVolatility = HistoricalVolatility
 module.exports.MACD = MACD
 module.exports.BollingerBands = BollingerBands
 module.exports.ATR = ATR
diff --git a/bindings/node/src/lib.rs b/bindings/node/src/lib.rs
index 6984d04d..13ab683f 100644
--- a/bindings/node/src/lib.rs
+++ b/bindings/node/src/lib.rs
@@ -108,6 +108,8 @@ node_scalar_indicator!(ZlemaNode, "ZLEMA", wc::Zlema);
 node_scalar_indicator!(MomNode, "MOM", wc::Mom);
 node_scalar_indicator!(CmoNode, "CMO", wc::Cmo);
 node_scalar_indicator!(DpoNode, "DPO", wc::Dpo);
+node_scalar_indicator!(StdDevNode, "StdDev", wc::StdDev);
+node_scalar_indicator!(UlcerIndexNode, "UlcerIndex", wc::UlcerIndex);
 
 // ============================== MACD ==============================
 
@@ -1145,6 +1147,99 @@ impl PmoNode {
 
 // ============================== VWMA ==============================
 
+// ============================== NATR ==============================
+
+#[napi(js_name = "NATR")]
+pub struct NatrNode {
+    inner: wc::Natr,
+}
+
+#[napi]
+impl NatrNode {
+    #[napi(constructor)]
+    pub fn new(period: u32) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::Natr::new(period as usize).map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, high: f64, low: f64, close: f64) -> napi::Result<Option<f64>> {
+        Ok(self.inner.update(cnd(high, low, close, 0.0)?))
+    }
+    #[napi]
+    pub fn batch(
+        &mut self,
+        high: Vec<f64>,
+        low: Vec<f64>,
+        close: Vec<f64>,
+    ) -> napi::Result<Vec<f64>> {
+        if high.len() != low.len() || low.len() != close.len() {
+            return Err(NapiError::from_reason(
+                "high, low, close must be equal length".to_string(),
+            ));
+        }
+        let mut out = Vec::with_capacity(high.len());
+        for i in 0..high.len() {
+            out.push(
+                self.inner
+                    .update(cnd(high[i], low[i], close[i], 0.0)?)
+                    .unwrap_or(f64::NAN),
+            );
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+// ============================== Historical Volatility ==============================
+
+#[napi(js_name = "HistoricalVolatility")]
+pub struct HistoricalVolatilityNode {
+    inner: wc::HistoricalVolatility,
+}
+
+#[napi]
+impl HistoricalVolatilityNode {
+    #[napi(constructor)]
+    pub fn new(period: u32, trading_periods: u32) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::HistoricalVolatility::new(period as usize, trading_periods as usize)
+                .map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    #[napi]
+    pub fn batch(&mut self, prices: Vec<f64>) -> Vec<f64> {
+        flatten(self.inner.batch(&prices))
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
 // ============================== Aroon Oscillator ==============================
 
 #[napi(js_name = "AroonOscillator")]
diff --git a/bindings/python/python/wickra/__init__.pyi b/bindings/python/python/wickra/__init__.pyi
index 970a3d03..1a4901a5 100644
--- a/bindings/python/python/wickra/__init__.pyi
+++ b/bindings/python/python/wickra/__init__.pyi
@@ -76,6 +76,59 @@ class TRIMA:
     @property
     def value(self) -> Optional[float]: ...
 
+class NATR:
+    def __init__(self, period: int = 14) -> None: ...
+    def update(self, candle: CandleLike) -> Optional[float]: ...
+    def batch(
+        self,
+        high: NDArray[np.float64],
+        low: NDArray[np.float64],
+        close: NDArray[np.float64],
+    ) -> NDArray[np.float64]: ...
+    def reset(self) -> None: ...
+    def is_ready(self) -> bool: ...
+    def warmup_period(self) -> int: ...
+    @property
+    def period(self) -> int: ...
+    @property
+    def value(self) -> Optional[float]: ...
+
+class StdDev:
+    def __init__(self, period: int = 20) -> None: ...
+    def update(self, value: float) -> Optional[float]: ...
+    def batch(self, prices: NDArray[np.float64]) -> NDArray[np.float64]: ...
+    def reset(self) -> None: ...
+    def is_ready(self) -> bool: ...
+    def warmup_period(self) -> int: ...
+    @property
+    def period(self) -> int: ...
+    @property
+    def value(self) -> Optional[float]: ...
+
+class UlcerIndex:
+    def __init__(self, period: int = 14) -> None: ...
+    def update(self, value: float) -> Optional[float]: ...
+    def batch(self, prices: NDArray[np.float64]) -> NDArray[np.float64]: ...
+    def reset(self) -> None: ...
+    def is_ready(self) -> bool: ...
+    def warmup_period(self) -> int: ...
+    @property
+    def period(self) -> int: ...
+    @property
+    def value(self) -> Optional[float]: ...
+
+class HistoricalVolatility:
+    def __init__(self, period: int = 20, trading_periods: int = 252) -> None: ...
+    def update(self, value: float) -> Optional[float]: ...
+    def batch(self, prices: NDArray[np.float64]) -> NDArray[np.float64]: ...
+    def reset(self) -> None: ...
+    def is_ready(self) -> bool: ...
+    def warmup_period(self) -> int: ...
+    @property
+    def periods(self) -> Tuple[int, int]: ...
+    @property
+    def value(self) -> Optional[float]: ...
+
 class AroonOscillator:
     def __init__(self, period: int = 14) -> None: ...
     def update(self, candle: CandleLike) -> Optional[float]: ...
diff --git a/bindings/python/src/lib.rs b/bindings/python/src/lib.rs
index a1f3f76c..1a69c877 100644
--- a/bindings/python/src/lib.rs
+++ b/bindings/python/src/lib.rs
@@ -1519,6 +1519,235 @@ impl PyAroon {
     }
 }
 
+// ============================== NATR ==============================
+
+#[pyclass(name = "NATR", module = "wickra._wickra")]
+#[derive(Clone)]
+struct PyNatr {
+    inner: wc::Natr,
+}
+
+#[pymethods]
+impl PyNatr {
+    #[new]
+    #[pyo3(signature = (period=14))]
+    fn new(period: usize) -> PyResult<Self> {
+        Ok(Self {
+            inner: wc::Natr::new(period).map_err(map_err)?,
+        })
+    }
+    fn update(&mut self, candle: &Bound<'_, PyAny>) -> PyResult<Option<f64>> {
+        let c = extract_candle(candle)?;
+        Ok(self.inner.update(c))
+    }
+    /// Batch over numpy columns: high, low, close (all 1-D, equal length).
+    fn batch<'py>(
+        &mut self,
+        py: Python<'py>,
+        high: PyReadonlyArray1<'py, f64>,
+        low: PyReadonlyArray1<'py, f64>,
+        close: PyReadonlyArray1<'py, f64>,
+    ) -> PyResult<Bound<'py, PyArray1<f64>>> {
+        let h = high
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        let l = low
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        let c = close
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        if h.len() != l.len() || l.len() != c.len() {
+            return Err(PyValueError::new_err(
+                "high, low, close must be equal length",
+            ));
+        }
+        let mut out = Vec::with_capacity(h.len());
+        for i in 0..h.len() {
+            let candle = wc::Candle::new(c[i], h[i], l[i], c[i], 0.0, 0).map_err(map_err)?;
+            out.push(self.inner.update(candle).unwrap_or(f64::NAN));
+        }
+        Ok(out.into_pyarray_bound(py))
+    }
+    #[getter]
+    fn period(&self) -> usize {
+        self.inner.period()
+    }
+    #[getter]
+    fn value(&self) -> Option<f64> {
+        self.inner.value()
+    }
+    fn reset(&mut self) {
+        self.inner.reset();
+    }
+    fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    fn warmup_period(&self) -> usize {
+        self.inner.warmup_period()
+    }
+    fn __repr__(&self) -> String {
+        format!("NATR(period={})", self.inner.period())
+    }
+}
+
+// ============================== StdDev ==============================
+
+#[pyclass(name = "StdDev", module = "wickra._wickra")]
+#[derive(Clone)]
+struct PyStdDev {
+    inner: wc::StdDev,
+}
+
+#[pymethods]
+impl PyStdDev {
+    #[new]
+    #[pyo3(signature = (period=20))]
+    fn new(period: usize) -> PyResult<Self> {
+        Ok(Self {
+            inner: wc::StdDev::new(period).map_err(map_err)?,
+        })
+    }
+    fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    fn batch<'py>(
+        &mut self,
+        py: Python<'py>,
+        prices: PyReadonlyArray1<'py, f64>,
+    ) -> PyResult<Bound<'py, PyArray1<f64>>> {
+        let slice = prices
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        Ok(flatten(self.inner.batch(slice)).into_pyarray_bound(py))
+    }
+    #[getter]
+    fn period(&self) -> usize {
+        self.inner.period()
+    }
+    #[getter]
+    fn value(&self) -> Option<f64> {
+        self.inner.value()
+    }
+    fn reset(&mut self) {
+        self.inner.reset();
+    }
+    fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    fn warmup_period(&self) -> usize {
+        self.inner.warmup_period()
+    }
+    fn __repr__(&self) -> String {
+        format!("StdDev(period={})", self.inner.period())
+    }
+}
+
+// ============================== Ulcer Index ==============================
+
+#[pyclass(name = "UlcerIndex", module = "wickra._wickra")]
+#[derive(Clone)]
+struct PyUlcerIndex {
+    inner: wc::UlcerIndex,
+}
+
+#[pymethods]
+impl PyUlcerIndex {
+    #[new]
+    #[pyo3(signature = (period=14))]
+    fn new(period: usize) -> PyResult<Self> {
+        Ok(Self {
+            inner: wc::UlcerIndex::new(period).map_err(map_err)?,
+        })
+    }
+    fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    fn batch<'py>(
+        &mut self,
+        py: Python<'py>,
+        prices: PyReadonlyArray1<'py, f64>,
+    ) -> PyResult<Bound<'py, PyArray1<f64>>> {
+        let slice = prices
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        Ok(flatten(self.inner.batch(slice)).into_pyarray_bound(py))
+    }
+    #[getter]
+    fn period(&self) -> usize {
+        self.inner.period()
+    }
+    #[getter]
+    fn value(&self) -> Option<f64> {
+        self.inner.value()
+    }
+    fn reset(&mut self) {
+        self.inner.reset();
+    }
+    fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    fn warmup_period(&self) -> usize {
+        self.inner.warmup_period()
+    }
+    fn __repr__(&self) -> String {
+        format!("UlcerIndex(period={})", self.inner.period())
+    }
+}
+
+// ============================== Historical Volatility ==============================
+
+#[pyclass(name = "HistoricalVolatility", module = "wickra._wickra")]
+#[derive(Clone)]
+struct PyHistoricalVolatility {
+    inner: wc::HistoricalVolatility,
+}
+
+#[pymethods]
+impl PyHistoricalVolatility {
+    #[new]
+    #[pyo3(signature = (period=20, trading_periods=252))]
+    fn new(period: usize, trading_periods: usize) -> PyResult<Self> {
+        Ok(Self {
+            inner: wc::HistoricalVolatility::new(period, trading_periods).map_err(map_err)?,
+        })
+    }
+    fn update(&mut self, value: f64) -> Option<f64> {
+        self.inner.update(value)
+    }
+    fn batch<'py>(
+        &mut self,
+        py: Python<'py>,
+        prices: PyReadonlyArray1<'py, f64>,
+    ) -> PyResult<Bound<'py, PyArray1<f64>>> {
+        let slice = prices
+            .as_slice()
+            .map_err(|_| PyValueError::new_err(NON_CONTIGUOUS))?;
+        Ok(flatten(self.inner.batch(slice)).into_pyarray_bound(py))
+    }
+    #[getter]
+    fn periods(&self) -> (usize, usize) {
+        self.inner.periods()
+    }
+    #[getter]
+    fn value(&self) -> Option<f64> {
+        self.inner.value()
+    }
+    fn reset(&mut self) {
+        self.inner.reset();
+    }
+    fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    fn warmup_period(&self) -> usize {
+        self.inner.warmup_period()
+    }
+    fn __repr__(&self) -> String {
+        let (p, t) = self.inner.periods();
+        format!("HistoricalVolatility(period={p}, trading_periods={t})")
+    }
+}
+
 // ============================== Aroon Oscillator ==============================
 
 #[pyclass(name = "AroonOscillator", module = "wickra._wickra")]
@@ -2556,5 +2785,9 @@ fn _wickra(_py: Python<'_>, m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_class::<PyAroonOscillator>()?;
     m.add_class::<PyVortex>()?;
     m.add_class::<PyMassIndex>()?;
+    m.add_class::<PyNatr>()?;
+    m.add_class::<PyStdDev>()?;
+    m.add_class::<PyUlcerIndex>()?;
+    m.add_class::<PyHistoricalVolatility>()?;
     Ok(())
 }
diff --git a/bindings/wasm/src/lib.rs b/bindings/wasm/src/lib.rs
index 95c51c20..d565bb31 100644
--- a/bindings/wasm/src/lib.rs
+++ b/bindings/wasm/src/lib.rs
@@ -87,6 +87,9 @@ wasm_scalar_indicator!(WasmStochRsi, "StochRSI", wc::StochRsi, rsi_period: usize
 wasm_scalar_indicator!(WasmDpo, "DPO", wc::Dpo, period: usize);
 wasm_scalar_indicator!(WasmPpo, "PPO", wc::Ppo, fast: usize, slow: usize);
 wasm_scalar_indicator!(WasmCoppock, "Coppock", wc::Coppock, roc_long: usize, roc_short: usize, wma_period: usize);
+wasm_scalar_indicator!(WasmStdDev, "StdDev", wc::StdDev, period: usize);
+wasm_scalar_indicator!(WasmUlcerIndex, "UlcerIndex", wc::UlcerIndex, period: usize);
+wasm_scalar_indicator!(WasmHistoricalVolatility, "HistoricalVolatility", wc::HistoricalVolatility, period: usize, trading_periods: usize);
 
 // ---------- KAMA (three params) ----------
 
@@ -372,6 +375,44 @@ impl WasmUltimateOscillator {
     }
 }
 
+#[wasm_bindgen(js_name = NATR)]
+pub struct WasmNatr {
+    inner: wc::Natr,
+}
+
+#[wasm_bindgen(js_class = NATR)]
+impl WasmNatr {
+    #[wasm_bindgen(constructor)]
+    pub fn new(period: usize) -> Result<WasmNatr, JsError> {
+        Ok(Self {
+            inner: wc::Natr::new(period).map_err(map_err)?,
+        })
+    }
+    pub fn update(&mut self, high: f64, low: f64, close: f64) -> Result<Option<f64>, JsError> {
+        let c = make_candle(high, low, close, 0.0)?;
+        Ok(self.inner.update(c))
+    }
+    pub fn batch(
+        &mut self,
+        high: &[f64],
+        low: &[f64],
+        close: &[f64],
+    ) -> Result<Float64Array, JsError> {
+        if high.len() != low.len() || low.len() != close.len() {
+            return Err(JsError::new("high, low, close must be equal length"));
+        }
+        let mut out = Vec::with_capacity(high.len());
+        for i in 0..high.len() {
+            let c = make_candle(high[i], low[i], close[i], 0.0)?;
+            out.push(self.inner.update(c).unwrap_or(f64::NAN));
+        }
+        Ok(Float64Array::from(out.as_slice()))
+    }
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+}
+
 #[wasm_bindgen(js_name = AroonOscillator)]
 pub struct WasmAroonOscillator {
     inner: wc::AroonOscillator,
diff --git a/crates/wickra-core/src/indicators/historical_volatility.rs b/crates/wickra-core/src/indicators/historical_volatility.rs
new file mode 100644
index 00000000..eafdb6f9
--- /dev/null
+++ b/crates/wickra-core/src/indicators/historical_volatility.rs
@@ -0,0 +1,253 @@
+//! Historical Volatility.
+
+use std::collections::VecDeque;
+
+use crate::error::{Error, Result};
+use crate::traits::Indicator;
+
+/// Historical Volatility — the annualised standard deviation of log returns.
+///
+/// This is the realised (backward-looking) volatility used to price options
+/// and size risk:
+///
+/// ```text
+/// r_t = ln(price_t / price_{t−1})
+/// HV  = stddev_sample(r over period) · √trading_periods · 100
+/// ```
+///
+/// The log returns over the window are measured with the **sample** standard
+/// deviation (divisor `n − 1`, the unbiased estimator), then scaled to an
+/// annual figure by `√trading_periods` — `252` for daily bars, `52` for
+/// weekly, `12` for monthly — and expressed as a percentage.
+///
+/// # Example
+///
+/// ```
+/// use wickra_core::{Indicator, HistoricalVolatility};
+///
+/// // 20-bar window, 252 trading days per year.
+/// let mut indicator = HistoricalVolatility::new(20, 252).unwrap();
+/// let mut last = None;
+/// for i in 0..80 {
+///     last = indicator.update(100.0 + (f64::from(i) * 0.3).sin() * 5.0);
+/// }
+/// assert!(last.is_some());
+/// ```
+#[derive(Debug, Clone)]
+pub struct HistoricalVolatility {
+    period: usize,
+    trading_periods: usize,
+    prev_price: Option<f64>,
+    /// Rolling window of the last `period` log returns.
+    window: VecDeque<f64>,
+    sum: f64,
+    sum_sq: f64,
+    last: Option<f64>,
+}
+
+impl HistoricalVolatility {
+    /// Construct a new Historical Volatility indicator.
+    ///
+    /// `period` is the number of log returns in the rolling window;
+    /// `trading_periods` is the annualisation factor (`252` daily, `52`
+    /// weekly, `12` monthly).
+    ///
+    /// # Errors
+    ///
+    /// Returns [`Error::PeriodZero`] if `period` or `trading_periods` is `0`,
+    /// or [`Error::InvalidPeriod`] if `period == 1` (the sample standard
+    /// deviation needs at least two returns).
+    pub fn new(period: usize, trading_periods: usize) -> Result<Self> {
+        if period == 0 || trading_periods == 0 {
+            return Err(Error::PeriodZero);
+        }
+        if period < 2 {
+            return Err(Error::InvalidPeriod {
+                message: "historical volatility period must be >= 2",
+            });
+        }
+        Ok(Self {
+            period,
+            trading_periods,
+            prev_price: None,
+            window: VecDeque::with_capacity(period),
+            sum: 0.0,
+            sum_sq: 0.0,
+            last: None,
+        })
+    }
+
+    /// Configured `(period, trading_periods)`.
+    pub const fn periods(&self) -> (usize, usize) {
+        (self.period, self.trading_periods)
+    }
+
+    /// Current value if available.
+    pub const fn value(&self) -> Option<f64> {
+        self.last
+    }
+}
+
+impl Indicator for HistoricalVolatility {
+    type Input = f64;
+    type Output = f64;
+
+    fn update(&mut self, input: f64) -> Option<f64> {
+        if !input.is_finite() {
+            // Non-finite input is ignored; state is left untouched.
+            return self.last;
+        }
+        let Some(prev) = self.prev_price else {
+            self.prev_price = Some(input);
+            return None;
+        };
+        self.prev_price = Some(input);
+
+        let log_return = if prev <= 0.0 || input <= 0.0 {
+            // Log return is undefined for non-positive prices.
+            0.0
+        } else {
+            (input / prev).ln()
+        };
+        if self.window.len() == self.period {
+            let old = self.window.pop_front().expect("window is non-empty");
+            self.sum -= old;
+            self.sum_sq -= old * old;
+        }
+        self.window.push_back(log_return);
+        self.sum += log_return;
+        self.sum_sq += log_return * log_return;
+        if self.window.len() < self.period {
+            return None;
+        }
+        let n = self.period as f64;
+        let mean = self.sum / n;
+        // Sample variance (Bessel's correction): Σ(x−mean)² / (n−1).
+        let variance = ((self.sum_sq - n * mean * mean) / (n - 1.0)).max(0.0);
+        let hv = variance.sqrt() * (self.trading_periods as f64).sqrt() * 100.0;
+        self.last = Some(hv);
+        Some(hv)
+    }
+
+    fn reset(&mut self) {
+        self.prev_price = None;
+        self.window.clear();
+        self.sum = 0.0;
+        self.sum_sq = 0.0;
+        self.last = None;
+    }
+
+    fn warmup_period(&self) -> usize {
+        // The first log return needs a previous price, then the window fills.
+        self.period + 1
+    }
+
+    fn is_ready(&self) -> bool {
+        self.last.is_some()
+    }
+
+    fn name(&self) -> &'static str {
+        "HistoricalVolatility"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::traits::BatchExt;
+    use approx::assert_relative_eq;
+
+    #[test]
+    fn new_rejects_zero_period() {
+        assert!(matches!(
+            HistoricalVolatility::new(0, 252),
+            Err(Error::PeriodZero)
+        ));
+        assert!(matches!(
+            HistoricalVolatility::new(20, 0),
+            Err(Error::PeriodZero)
+        ));
+    }
+
+    #[test]
+    fn new_rejects_period_one() {
+        assert!(matches!(
+            HistoricalVolatility::new(1, 252),
+            Err(Error::InvalidPeriod { .. })
+        ));
+    }
+
+    #[test]
+    fn first_emission_at_warmup_period() {
+        let mut hv = HistoricalVolatility::new(5, 252).unwrap();
+        assert_eq!(hv.warmup_period(), 6);
+        let out = hv.batch(&(1..=20).map(f64::from).collect::<Vec<_>>());
+        for v in out.iter().take(5) {
+            assert!(v.is_none());
+        }
+        assert!(out[5].is_some());
+    }
+
+    #[test]
+    fn constant_series_yields_zero() {
+        // Flat prices -> all log returns are 0 -> zero volatility.
+        let mut hv = HistoricalVolatility::new(10, 252).unwrap();
+        let out = hv.batch(&[100.0; 40]);
+        for v in out.iter().skip(10).flatten() {
+            assert_relative_eq!(*v, 0.0, epsilon = 1e-12);
+        }
+    }
+
+    #[test]
+    fn geometric_series_yields_zero() {
+        // A constant growth factor gives a constant log return -> zero stddev.
+        let mut hv = HistoricalVolatility::new(10, 252).unwrap();
+        let prices: Vec<f64> = (0..40).map(|i| 100.0 * 1.01_f64.powi(i)).collect();
+        let out = hv.batch(&prices);
+        for v in out.iter().skip(10).flatten() {
+            assert_relative_eq!(*v, 0.0, epsilon = 1e-9);
+        }
+    }
+
+    #[test]
+    fn output_is_non_negative() {
+        let mut hv = HistoricalVolatility::new(20, 252).unwrap();
+        let prices: Vec<f64> = (1..=200)
+            .map(|i| 100.0 + (f64::from(i) * 0.3).sin() * 12.0)
+            .collect();
+        for v in hv.batch(&prices).into_iter().flatten() {
+            assert!(v >= 0.0, "volatility must be non-negative, got {v}");
+        }
+    }
+
+    #[test]
+    fn ignores_non_finite_input() {
+        let mut hv = HistoricalVolatility::new(5, 252).unwrap();
+        let out = hv.batch(&(1..=20).map(f64::from).collect::<Vec<_>>());
+        let last = *out.last().unwrap();
+        assert!(last.is_some());
+        assert_eq!(hv.update(f64::NAN), last);
+        assert_eq!(hv.update(f64::INFINITY), last);
+    }
+
+    #[test]
+    fn reset_clears_state() {
+        let mut hv = HistoricalVolatility::new(5, 252).unwrap();
+        hv.batch(&(1..=20).map(f64::from).collect::<Vec<_>>());
+        assert!(hv.is_ready());
+        hv.reset();
+        assert!(!hv.is_ready());
+        assert_eq!(hv.update(1.0), None);
+    }
+
+    #[test]
+    fn batch_equals_streaming() {
+        let prices: Vec<f64> = (1..=120)
+            .map(|i| 100.0 + (f64::from(i) * 0.25).sin() * 9.0)
+            .collect();
+        let batch = HistoricalVolatility::new(20, 252).unwrap().batch(&prices);
+        let mut b = HistoricalVolatility::new(20, 252).unwrap();
+        let streamed: Vec<_> = prices.iter().map(|p| b.update(*p)).collect();
+        assert_eq!(batch, streamed);
+    }
+}
diff --git a/crates/wickra-core/src/indicators/mod.rs b/crates/wickra-core/src/indicators/mod.rs
index 9e2248a6..0c1ec701 100644
--- a/crates/wickra-core/src/indicators/mod.rs
+++ b/crates/wickra-core/src/indicators/mod.rs
@@ -17,6 +17,7 @@ mod dema;
 mod donchian;
 mod dpo;
 mod ema;
+mod historical_volatility;
 mod hma;
 mod kama;
 mod keltner;
@@ -24,6 +25,7 @@ mod macd;
 mod mass_index;
 mod mfi;
 mod mom;
+mod natr;
 mod obv;
 mod pmo;
 mod ppo;
@@ -32,6 +34,7 @@ mod roc;
 mod rsi;
 mod sma;
 mod smma;
+mod std_dev;
 mod stoch_rsi;
 mod stochastic;
 mod t3;
@@ -39,6 +42,7 @@ mod tema;
 mod trima;
 mod trix;
 mod tsi;
+mod ulcer_index;
 mod ultimate_oscillator;
 mod vortex;
 mod vwap;
@@ -60,6 +64,7 @@ pub use dema::Dema;
 pub use donchian::{Donchian, DonchianOutput};
 pub use dpo::Dpo;
 pub use ema::Ema;
+pub use historical_volatility::HistoricalVolatility;
 pub use hma::Hma;
 pub use kama::Kama;
 pub use keltner::{Keltner, KeltnerOutput};
@@ -67,6 +72,7 @@ pub use macd::{MacdIndicator, MacdOutput};
 pub use mass_index::MassIndex;
 pub use mfi::Mfi;
 pub use mom::Mom;
+pub use natr::Natr;
 pub use obv::Obv;
 pub use pmo::Pmo;
 pub use ppo::Ppo;
@@ -75,6 +81,7 @@ pub use roc::Roc;
 pub use rsi::Rsi;
 pub use sma::Sma;
 pub use smma::Smma;
+pub use std_dev::StdDev;
 pub use stoch_rsi::StochRsi;
 pub use stochastic::{Stochastic, StochasticOutput};
 pub use t3::T3;
@@ -82,6 +89,7 @@ pub use tema::Tema;
 pub use trima::Trima;
 pub use trix::Trix;
 pub use tsi::Tsi;
+pub use ulcer_index::UlcerIndex;
 pub use ultimate_oscillator::UltimateOscillator;
 pub use vortex::{Vortex, VortexOutput};
 pub use vwap::{RollingVwap, Vwap};
diff --git a/crates/wickra-core/src/indicators/natr.rs b/crates/wickra-core/src/indicators/natr.rs
new file mode 100644
index 00000000..8a80cca0
--- /dev/null
+++ b/crates/wickra-core/src/indicators/natr.rs
@@ -0,0 +1,185 @@
+//! Normalized Average True Range.
+
+use crate::error::Result;
+use crate::ohlcv::Candle;
+use crate::traits::Indicator;
+
+use super::Atr;
+
+/// Normalized Average True Range — [`Atr`] expressed as a percentage of price.
+///
+/// `Atr` reports volatility in raw price units, which makes its readings
+/// impossible to compare across instruments at different price levels. NATR
+/// fixes that by dividing by the current close:
+///
+/// ```text
+/// NATR = 100 · ATR / close
+/// ```
+///
+/// A NATR of `2.0` always means "the average true range is 2 % of price",
+/// whether the instrument trades at $10 or $10 000 — so NATR values are
+/// directly comparable, and stop distances or position sizes expressed as a
+/// NATR multiple behave consistently across a portfolio.
+///
+/// # Example
+///
+/// ```
+/// use wickra_core::{Candle, Indicator, Natr};
+///
+/// let mut indicator = Natr::new(14).unwrap();
+/// let mut last = None;
+/// for i in 0..80 {
+///     let base = 100.0 + f64::from(i);
+///     let candle =
+///         Candle::new(base, base + 2.0, base - 2.0, base, 10.0, i64::from(i)).unwrap();
+///     last = indicator.update(candle);
+/// }
+/// assert!(last.is_some());
+/// ```
+#[derive(Debug, Clone)]
+pub struct Natr {
+    atr: Atr,
+    last: Option<f64>,
+}
+
+impl Natr {
+    /// Construct a new NATR with the given ATR period.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`crate::Error::PeriodZero`] if `period == 0`.
+    pub fn new(period: usize) -> Result<Self> {
+        Ok(Self {
+            atr: Atr::new(period)?,
+            last: None,
+        })
+    }
+
+    /// Configured period.
+    pub const fn period(&self) -> usize {
+        self.atr.period()
+    }
+
+    /// Current value if available.
+    pub const fn value(&self) -> Option<f64> {
+        self.last
+    }
+}
+
+impl Indicator for Natr {
+    type Input = Candle;
+    type Output = f64;
+
+    fn update(&mut self, candle: Candle) -> Option<f64> {
+        let atr = self.atr.update(candle)?;
+        let natr = if candle.close == 0.0 {
+            // NATR is undefined against a zero close.
+            0.0
+        } else {
+            100.0 * atr / candle.close
+        };
+        self.last = Some(natr);
+        Some(natr)
+    }
+
+    fn reset(&mut self) {
+        self.atr.reset();
+        self.last = None;
+    }
+
+    fn warmup_period(&self) -> usize {
+        self.atr.warmup_period()
+    }
+
+    fn is_ready(&self) -> bool {
+        self.last.is_some()
+    }
+
+    fn name(&self) -> &'static str {
+        "NATR"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::traits::BatchExt;
+    use approx::assert_relative_eq;
+
+    fn candle(open: f64, high: f64, low: f64, close: f64, ts: i64) -> Candle {
+        Candle::new(open, high, low, close, 1.0, ts).unwrap()
+    }
+
+    #[test]
+    fn new_rejects_zero_period() {
+        assert!(Natr::new(0).is_err());
+    }
+
+    #[test]
+    fn warmup_period_matches_atr() {
+        let natr = Natr::new(14).unwrap();
+        assert_eq!(natr.warmup_period(), 14);
+    }
+
+    #[test]
+    fn natr_is_atr_over_close_as_percent() {
+        // NATR must equal 100 * ATR / close, bar for bar.
+        let candles: Vec<Candle> = (0..60)
+            .map(|i| {
+                let mid = 100.0 + (i as f64 * 0.3).sin() * 10.0;
+                candle(mid, mid + 3.0, mid - 3.0, mid + 1.0, i)
+            })
+            .collect();
+        let natr_out = Natr::new(14).unwrap().batch(&candles);
+        let atr_out = Atr::new(14).unwrap().batch(&candles);
+        for (i, (n, a)) in natr_out.iter().zip(atr_out.iter()).enumerate() {
+            match (n, a) {
+                (Some(nv), Some(av)) => {
+                    let want = 100.0 * av / candles[i].close;
+                    assert_relative_eq!(*nv, want, epsilon = 1e-9);
+                }
+                (None, None) => {}
+                _ => panic!("warmup mismatch at {i}"),
+            }
+        }
+    }
+
+    #[test]
+    fn flat_market_yields_zero() {
+        // No range -> ATR is 0 -> NATR is 0.
+        let mut natr = Natr::new(5).unwrap();
+        let candles: Vec<Candle> = (0..30)
+            .map(|i| candle(100.0, 100.0, 100.0, 100.0, i))
+            .collect();
+        for v in natr.batch(&candles).into_iter().flatten() {
+            assert_relative_eq!(v, 0.0, epsilon = 1e-12);
+        }
+    }
+
+    #[test]
+    fn reset_clears_state() {
+        let mut natr = Natr::new(5).unwrap();
+        let candles: Vec<Candle> = (0..20)
+            .map(|i| candle(100.0, 102.0, 98.0, 101.0, i))
+            .collect();
+        natr.batch(&candles);
+        assert!(natr.is_ready());
+        natr.reset();
+        assert!(!natr.is_ready());
+        assert_eq!(natr.update(candles[0]), None);
+    }
+
+    #[test]
+    fn batch_equals_streaming() {
+        let candles: Vec<Candle> = (0..80)
+            .map(|i| {
+                let mid = 100.0 + (i as f64 * 0.35).sin() * 9.0;
+                candle(mid, mid + 2.5, mid - 2.5, mid + 0.5, i)
+            })
+            .collect();
+        let batch = Natr::new(14).unwrap().batch(&candles);
+        let mut b = Natr::new(14).unwrap();
+        let streamed: Vec<_> = candles.iter().map(|c| b.update(*c)).collect();
+        assert_eq!(batch, streamed);
+    }
+}
diff --git a/crates/wickra-core/src/indicators/std_dev.rs b/crates/wickra-core/src/indicators/std_dev.rs
new file mode 100644
index 00000000..bec83f1b
--- /dev/null
+++ b/crates/wickra-core/src/indicators/std_dev.rs
@@ -0,0 +1,200 @@
+//! Rolling population standard deviation.
+
+use std::collections::VecDeque;
+
+use crate::error::{Error, Result};
+use crate::traits::Indicator;
+
+/// Rolling population standard deviation over the last `period` values.
+///
+/// ```text
+/// mean     = (1/n) · Σ price
+/// variance = (1/n) · Σ price² − mean²
+/// StdDev   = √variance
+/// ```
+///
+/// This is the **population** standard deviation (divisor `n`, not `n − 1`) —
+/// the same dispersion measure that drives [`BollingerBands`](crate::BollingerBands).
+/// It is maintained as an O(1) rolling state machine: a running sum and a
+/// running sum-of-squares, updated by one add and one subtract per bar. Tiny
+/// negative variances from floating-point cancellation are clamped to zero
+/// before the square root.
+///
+/// # Example
+///
+/// ```
+/// use wickra_core::{Indicator, StdDev};
+///
+/// let mut indicator = StdDev::new(20).unwrap();
+/// let mut last = None;
+/// for i in 0..80 {
+///     last = indicator.update(100.0 + (f64::from(i) * 0.3).sin() * 5.0);
+/// }
+/// assert!(last.is_some());
+/// ```
+#[derive(Debug, Clone)]
+pub struct StdDev {
+    period: usize,
+    window: VecDeque<f64>,
+    sum: f64,
+    sum_sq: f64,
+    last: Option<f64>,
+}
+
+impl StdDev {
+    /// Construct a new rolling standard deviation with the given period.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`Error::PeriodZero`] if `period == 0`.
+    pub fn new(period: usize) -> Result<Self> {
+        if period == 0 {
+            return Err(Error::PeriodZero);
+        }
+        Ok(Self {
+            period,
+            window: VecDeque::with_capacity(period),
+            sum: 0.0,
+            sum_sq: 0.0,
+            last: None,
+        })
+    }
+
+    /// Configured period.
+    pub const fn period(&self) -> usize {
+        self.period
+    }
+
+    /// Current value if available.
+    pub const fn value(&self) -> Option<f64> {
+        self.last
+    }
+}
+
+impl Indicator for StdDev {
+    type Input = f64;
+    type Output = f64;
+
+    fn update(&mut self, input: f64) -> Option<f64> {
+        if !input.is_finite() {
+            // Non-finite input is ignored; the window is left untouched.
+            return self.last;
+        }
+        if self.window.len() == self.period {
+            let old = self.window.pop_front().expect("window is non-empty");
+            self.sum -= old;
+            self.sum_sq -= old * old;
+        }
+        self.window.push_back(input);
+        self.sum += input;
+        self.sum_sq += input * input;
+        if self.window.len() < self.period {
+            return None;
+        }
+        let n = self.period as f64;
+        let mean = self.sum / n;
+        // Clamp floating-point cancellation noise: variance is never negative.
+        let variance = (self.sum_sq / n - mean * mean).max(0.0);
+        let sd = variance.sqrt();
+        self.last = Some(sd);
+        Some(sd)
+    }
+
+    fn reset(&mut self) {
+        self.window.clear();
+        self.sum = 0.0;
+        self.sum_sq = 0.0;
+        self.last = None;
+    }
+
+    fn warmup_period(&self) -> usize {
+        self.period
+    }
+
+    fn is_ready(&self) -> bool {
+        self.last.is_some()
+    }
+
+    fn name(&self) -> &'static str {
+        "StdDev"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::traits::BatchExt;
+    use approx::assert_relative_eq;
+
+    #[test]
+    fn new_rejects_zero_period() {
+        assert!(matches!(StdDev::new(0), Err(Error::PeriodZero)));
+    }
+
+    #[test]
+    fn reference_value() {
+        // StdDev(3) of [2, 4, 6]: mean = 4, variance = (4+0+4)/3 = 8/3.
+        let mut sd = StdDev::new(3).unwrap();
+        let out = sd.batch(&[2.0, 4.0, 6.0]);
+        assert_eq!(out[0], None);
+        assert_eq!(out[1], None);
+        assert_relative_eq!(out[2].unwrap(), (8.0_f64 / 3.0).sqrt(), epsilon = 1e-12);
+    }
+
+    #[test]
+    fn constant_series_yields_zero() {
+        let mut sd = StdDev::new(5).unwrap();
+        let out = sd.batch(&[42.0; 20]);
+        for v in out.iter().skip(4).flatten() {
+            assert_relative_eq!(*v, 0.0, epsilon = 1e-12);
+        }
+    }
+
+    #[test]
+    fn matches_naive_definition() {
+        let prices: Vec<f64> = (1..=60)
+            .map(|i| 100.0 + (f64::from(i) * 0.4).sin() * 8.0)
+            .collect();
+        let period = 10;
+        let got = StdDev::new(period).unwrap().batch(&prices);
+        for (i, g) in got.iter().enumerate() {
+            if let Some(value) = g {
+                let window = &prices[i + 1 - period..=i];
+                let mean = window.iter().sum::<f64>() / period as f64;
+                let var = window.iter().map(|x| (x - mean).powi(2)).sum::<f64>() / period as f64;
+                assert_relative_eq!(*value, var.sqrt(), epsilon = 1e-9);
+            }
+        }
+    }
+
+    #[test]
+    fn ignores_non_finite_input() {
+        let mut sd = StdDev::new(3).unwrap();
+        let out = sd.batch(&[2.0, 4.0, 6.0]);
+        let last = out[2];
+        assert!(last.is_some());
+        assert_eq!(sd.update(f64::NAN), last);
+        assert_eq!(sd.update(f64::INFINITY), last);
+    }
+
+    #[test]
+    fn reset_clears_state() {
+        let mut sd = StdDev::new(3).unwrap();
+        sd.batch(&[1.0, 2.0, 3.0, 4.0]);
+        assert!(sd.is_ready());
+        sd.reset();
+        assert!(!sd.is_ready());
+        assert_eq!(sd.update(1.0), None);
+    }
+
+    #[test]
+    fn batch_equals_streaming() {
+        let prices: Vec<f64> = (1..=60)
+            .map(|i| 100.0 + (f64::from(i) * 0.3).cos() * 7.0)
+            .collect();
+        let batch = StdDev::new(14).unwrap().batch(&prices);
+        let mut b = StdDev::new(14).unwrap();
+        let streamed: Vec<_> = prices.iter().map(|p| b.update(*p)).collect();
+        assert_eq!(batch, streamed);
+    }
+}
diff --git a/crates/wickra-core/src/indicators/ulcer_index.rs b/crates/wickra-core/src/indicators/ulcer_index.rs
new file mode 100644
index 00000000..0a5337eb
--- /dev/null
+++ b/crates/wickra-core/src/indicators/ulcer_index.rs
@@ -0,0 +1,229 @@
+//! Ulcer Index.
+
+use std::collections::VecDeque;
+
+use crate::error::{Error, Result};
+use crate::traits::Indicator;
+
+/// Ulcer Index — Peter Martin's downside-only volatility / risk measure.
+///
+/// Standard deviation punishes upside and downside moves equally; the Ulcer
+/// Index measures only the **pain of drawdowns**. For each bar it computes the
+/// percentage drop from the highest price of the trailing window, squares it,
+/// and reports the root-mean-square over the window:
+///
+/// ```text
+/// drawdown_t = 100 · (price_t − max(price, period)_t) / max(price, period)_t
+/// UlcerIndex = √( mean( drawdown² over period ) )
+/// ```
+///
+/// A pure up-trend never trades below its own running high, so its Ulcer Index
+/// is `0`; the deeper and longer the drawdowns, the higher the reading. It is
+/// the volatility measure of choice for risk-adjusted return ratios (the
+/// "Martin ratio" / UPI).
+///
+/// # Example
+///
+/// ```
+/// use wickra_core::{Indicator, UlcerIndex};
+///
+/// let mut indicator = UlcerIndex::new(14).unwrap();
+/// let mut last = None;
+/// for i in 0..80 {
+///     last = indicator.update(100.0 + (f64::from(i) * 0.3).sin() * 8.0);
+/// }
+/// assert!(last.is_some());
+/// ```
+#[derive(Debug, Clone)]
+pub struct UlcerIndex {
+    period: usize,
+    /// Rolling window of the last `period` prices (for the trailing maximum).
+    prices: VecDeque<f64>,
+    /// Rolling window of the last `period` squared percentage drawdowns.
+    drawdowns_sq: VecDeque<f64>,
+    sum_sq: f64,
+    last: Option<f64>,
+}
+
+impl UlcerIndex {
+    /// Construct a new Ulcer Index with the given period.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`Error::PeriodZero`] if `period == 0`.
+    pub fn new(period: usize) -> Result<Self> {
+        if period == 0 {
+            return Err(Error::PeriodZero);
+        }
+        Ok(Self {
+            period,
+            prices: VecDeque::with_capacity(period),
+            drawdowns_sq: VecDeque::with_capacity(period),
+            sum_sq: 0.0,
+            last: None,
+        })
+    }
+
+    /// Configured period.
+    pub const fn period(&self) -> usize {
+        self.period
+    }
+
+    /// Current value if available.
+    pub const fn value(&self) -> Option<f64> {
+        self.last
+    }
+}
+
+impl Indicator for UlcerIndex {
+    type Input = f64;
+    type Output = f64;
+
+    fn update(&mut self, input: f64) -> Option<f64> {
+        if !input.is_finite() {
+            // Non-finite input is ignored; state is left untouched.
+            return self.last;
+        }
+        if self.prices.len() == self.period {
+            self.prices.pop_front();
+        }
+        self.prices.push_back(input);
+        if self.prices.len() < self.period {
+            return None;
+        }
+        let max_price = self
+            .prices
+            .iter()
+            .copied()
+            .fold(f64::NEG_INFINITY, f64::max);
+        let drawdown = if max_price == 0.0 {
+            0.0
+        } else {
+            100.0 * (input - max_price) / max_price
+        };
+        let sq = drawdown * drawdown;
+
+        if self.drawdowns_sq.len() == self.period {
+            self.sum_sq -= self.drawdowns_sq.pop_front().expect("window is non-empty");
+        }
+        self.drawdowns_sq.push_back(sq);
+        self.sum_sq += sq;
+        if self.drawdowns_sq.len() < self.period {
+            return None;
+        }
+        let ui = (self.sum_sq / self.period as f64).sqrt();
+        self.last = Some(ui);
+        Some(ui)
+    }
+
+    fn reset(&mut self) {
+        self.prices.clear();
+        self.drawdowns_sq.clear();
+        self.sum_sq = 0.0;
+        self.last = None;
+    }
+
+    fn warmup_period(&self) -> usize {
+        // `period` prices fill the trailing-max window, then `period` squared
+        // drawdowns fill the RMS window.
+        2 * self.period - 1
+    }
+
+    fn is_ready(&self) -> bool {
+        self.last.is_some()
+    }
+
+    fn name(&self) -> &'static str {
+        "UlcerIndex"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::traits::BatchExt;
+    use approx::assert_relative_eq;
+
+    #[test]
+    fn new_rejects_zero_period() {
+        assert!(matches!(UlcerIndex::new(0), Err(Error::PeriodZero)));
+    }
+
+    #[test]
+    fn reference_values() {
+        // UlcerIndex(2): warmup = 3.
+        // [10, 8, 12, 9]:
+        //   bar 3: window [8,12], max 12, drawdown 0; sq window [400, 0]
+        //          -> UI = sqrt(200).
+        //   bar 4: window [12,9], max 12, drawdown -25, sq 625; sq window [0, 625]
+        //          -> UI = sqrt(312.5).
+        let mut ui = UlcerIndex::new(2).unwrap();
+        let out = ui.batch(&[10.0, 8.0, 12.0, 9.0]);
+        assert_eq!(ui.warmup_period(), 3);
+        assert_eq!(out[0], None);
+        assert_eq!(out[1], None);
+        assert_relative_eq!(out[2].unwrap(), 200.0_f64.sqrt(), epsilon = 1e-12);
+        assert_relative_eq!(out[3].unwrap(), 312.5_f64.sqrt(), epsilon = 1e-12);
+    }
+
+    #[test]
+    fn pure_uptrend_yields_zero() {
+        // Price never trades below its own running high: no drawdown at all.
+        let mut ui = UlcerIndex::new(5).unwrap();
+        let out = ui.batch(&(1..=40).map(f64::from).collect::<Vec<_>>());
+        for v in out.iter().skip(ui.warmup_period() - 1).flatten() {
+            assert_relative_eq!(*v, 0.0, epsilon = 1e-12);
+        }
+    }
+
+    #[test]
+    fn constant_series_yields_zero() {
+        let mut ui = UlcerIndex::new(5).unwrap();
+        let out = ui.batch(&[50.0; 30]);
+        for v in out.iter().skip(ui.warmup_period() - 1).flatten() {
+            assert_relative_eq!(*v, 0.0, epsilon = 1e-12);
+        }
+    }
+
+    #[test]
+    fn output_is_non_negative() {
+        let mut ui = UlcerIndex::new(14).unwrap();
+        let prices: Vec<f64> = (1..=120)
+            .map(|i| 100.0 + (f64::from(i) * 0.25).sin() * 15.0)
+            .collect();
+        for v in ui.batch(&prices).into_iter().flatten() {
+            assert!(v >= 0.0, "Ulcer Index must be non-negative, got {v}");
+        }
+    }
+
+    #[test]
+    fn ignores_non_finite_input() {
+        let mut ui = UlcerIndex::new(2).unwrap();
+        let out = ui.batch(&[10.0, 8.0, 12.0, 9.0]);
+        let last = *out.last().unwrap();
+        assert!(last.is_some());
+        assert_eq!(ui.update(f64::NAN), last);
+        assert_eq!(ui.update(f64::INFINITY), last);
+    }
+
+    #[test]
+    fn reset_clears_state() {
+        let mut ui = UlcerIndex::new(3).unwrap();
+        ui.batch(&[10.0, 8.0, 12.0, 9.0, 11.0, 7.0]);
+        assert!(ui.is_ready());
+        ui.reset();
+        assert!(!ui.is_ready());
+        assert_eq!(ui.update(10.0), None);
+    }
+
+    #[test]
+    fn batch_equals_streaming() {
+        let prices: Vec<f64> = (1..=80)
+            .map(|i| 100.0 + (f64::from(i) * 0.3).sin() * 10.0)
+            .collect();
+        let batch = UlcerIndex::new(14).unwrap().batch(&prices);
+        let mut b = UlcerIndex::new(14).unwrap();
+        let streamed: Vec<_> = prices.iter().map(|p| b.update(*p)).collect();
+        assert_eq!(batch, streamed);
+    }
+}
diff --git a/crates/wickra-core/src/lib.rs b/crates/wickra-core/src/lib.rs
index 6d3dd005..4d2358b9 100644
--- a/crates/wickra-core/src/lib.rs
+++ b/crates/wickra-core/src/lib.rs
@@ -45,10 +45,11 @@ pub mod indicators;
 pub use error::{Error, Result};
 pub use indicators::{
     Adx, AdxOutput, Aroon, AroonOscillator, AroonOutput, Atr, AwesomeOscillator, BollingerBands,
-    BollingerOutput, Cci, Cmo, Coppock, Dema, Donchian, DonchianOutput, Dpo, Ema, Hma, Kama,
-    Keltner, KeltnerOutput, MacdIndicator, MacdOutput, MassIndex, Mfi, Mom, Obv, Pmo, Ppo, Psar,
-    Roc, RollingVwap, Rsi, Sma, Smma, StochRsi, Stochastic, StochasticOutput, Tema, Trima, Trix,
-    Tsi, UltimateOscillator, Vortex, VortexOutput, Vwap, Vwma, WilliamsR, Wma, Zlema, T3,
+    BollingerOutput, Cci, Cmo, Coppock, Dema, Donchian, DonchianOutput, Dpo, Ema,
+    HistoricalVolatility, Hma, Kama, Keltner, KeltnerOutput, MacdIndicator, MacdOutput, MassIndex,
+    Mfi, Mom, Natr, Obv, Pmo, Ppo, Psar, Roc, RollingVwap, Rsi, Sma, Smma, StdDev, StochRsi,
+    Stochastic, StochasticOutput, Tema, Trima, Trix, Tsi, UlcerIndex, UltimateOscillator, Vortex,
+    VortexOutput, Vwap, Vwma, WilliamsR, Wma, Zlema, T3,
 };
 pub use ohlcv::{Candle, Tick};
 pub use traits::{BatchExt, Chain, Indicator};
diff --git a/docs/wiki/Home.md b/docs/wiki/Home.md
index 1951d1b7..90e9ed1e 100644
--- a/docs/wiki/Home.md
+++ b/docs/wiki/Home.md
@@ -118,6 +118,10 @@ Rust / Python / Node examples. They are grouped by family, mirroring the
 - [Indicator-Keltner.md](indicators/volatility/Indicator-Keltner.md)
 - [Indicator-Donchian.md](indicators/volatility/Indicator-Donchian.md)
 - [Indicator-Psar.md](indicators/volatility/Indicator-Psar.md)
+- [Indicator-Natr.md](indicators/volatility/Indicator-Natr.md)
+- [Indicator-StdDev.md](indicators/volatility/Indicator-StdDev.md)
+- [Indicator-UlcerIndex.md](indicators/volatility/Indicator-UlcerIndex.md)
+- [Indicator-HistoricalVolatility.md](indicators/volatility/Indicator-HistoricalVolatility.md)
 
 **Volume** — price moves weighted or confirmed by traded volume.
 
diff --git a/docs/wiki/Indicators-Overview.md b/docs/wiki/Indicators-Overview.md
index d3dc1d7f..e52c3523 100644
--- a/docs/wiki/Indicators-Overview.md
+++ b/docs/wiki/Indicators-Overview.md
@@ -1,6 +1,6 @@
 # Indicators Overview
 
-Wickra ships 42 indicators, organised in source under the four classical
+Wickra ships 46 indicators, organised in source under the four classical
 families — trend, momentum, volatility, volume — that map directly to the
 directory structure of `crates/wickra-core/src/indicators/`. The same family
 labels are used here, plus a second-level grouping that reflects how the
@@ -136,6 +136,10 @@ measure — that lives in the volatility module by source convention.
 | Indicator | One-liner | Input | Output | Range | Defaults | Warmup | Deep dive |
 |-----------|-----------|-------|--------|-------|----------|--------|-----------|
 | `Atr`     | Wilder-smoothed True Range; per-bar absolute volatility. | `Candle` | `f64` | `[0, ∞)` (price scale) | `period = 14` (Python) | `period` | [Indicator-Atr.md](indicators/volatility/Indicator-Atr.md) |
+| `Natr`    | `100·ATR/close`; ATR as a percentage, comparable across instruments. | `Candle` | `f64` | `[0, ∞)` (percent) | `period = 14` (Python) | `period` | [Indicator-Natr.md](indicators/volatility/Indicator-Natr.md) |
+| `StdDev`  | Rolling population standard deviation of price. | `f64` | `f64` | `[0, ∞)` (price scale) | `period = 20` (Python) | `period` | [Indicator-StdDev.md](indicators/volatility/Indicator-StdDev.md) |
+| `UlcerIndex` | RMS of trailing-high drawdowns; downside-only risk. | `f64` | `f64` | `[0, ∞)` (percent) | `period = 14` (Python) | `2·period − 1` | [Indicator-UlcerIndex.md](indicators/volatility/Indicator-UlcerIndex.md) |
+| `HistoricalVolatility` | Annualised sample stddev of log returns. | `f64` | `f64` | `[0, ∞)` (annualised percent) | `(period=20, trading_periods=252)` (Python) | `period + 1` | [Indicator-HistoricalVolatility.md](indicators/volatility/Indicator-HistoricalVolatility.md) |
 
 ### Trailing stop
 
diff --git a/docs/wiki/indicators/volatility/Indicator-HistoricalVolatility.md b/docs/wiki/indicators/volatility/Indicator-HistoricalVolatility.md
new file mode 100644
index 00000000..31d794b6
--- /dev/null
+++ b/docs/wiki/indicators/volatility/Indicator-HistoricalVolatility.md
@@ -0,0 +1,166 @@
+# HistoricalVolatility
+
+> Historical Volatility — the annualised standard deviation of log returns,
+> the realised volatility used to price options and size risk.
+
+## Quick reference
+
+| Field | Value |
+|-------|-------|
+| Family | Volatility |
+| Sub-category | Return-based |
+| Input type | `f64` (single close) |
+| Output type | `f64` |
+| Output range | `[0, ∞)` (annualised percent) |
+| Default parameters | `(period = 20, trading_periods = 252)` (Python) |
+| Warmup period | `period + 1` |
+| Interpretation | Annualised volatility of returns, in percent. |
+
+## Formula
+
+```
+r_t = ln(price_t / price_{t−1})
+HV  = stddev_sample(r over period) · √trading_periods · 100
+```
+
+The log returns over the window are measured with the **sample** standard
+deviation (divisor `n − 1`, Bessel's correction — the unbiased volatility
+estimator), then annualised by `√trading_periods` and expressed as a
+percentage. `trading_periods` is the number of bars in a year for the
+data's frequency: `252` for daily bars, `52` for weekly, `12` for
+monthly.
+
+## Parameters
+
+| Name              | Type    | Default        | Valid range | Description |
+|-------------------|---------|----------------|-------------|-------------|
+| `period`          | `usize` | `20` (Python)  | `>= 2`      | Number of log returns in the window. `0` errors with `Error::PeriodZero`; `1` with `Error::InvalidPeriod` (the sample stddev needs two returns). |
+| `trading_periods` | `usize` | `252` (Python) | `>= 1`      | Annualisation factor. `0` errors with `Error::PeriodZero`. |
+
+The Python binding defaults the pair to `(20, 252)`. The `periods`
+property returns `(period, trading_periods)`.
+
+## Inputs / Outputs
+
+From `crates/wickra-core/src/indicators/historical_volatility.rs`:
+
+```rust
+impl Indicator for HistoricalVolatility {
+    type Input = f64;
+    type Output = f64;
+    // update(&mut self, input: f64) -> Option<f64>
+}
+```
+
+A single `f64` close in, an `Option<f64>` out. Python maps this to
+`float | None` / `numpy.ndarray` (NaN warmup); Node to `number | null` /
+`Array<number>` (NaN warmup).
+
+## Warmup
+
+`warmup_period() == period + 1`. The first log return needs a previous
+price, and the window must then hold `period` returns — so the first
+non-`None` output lands on input `period + 1`.
+
+## Edge cases
+
+- **Constant series.** A flat price series has all log returns equal to
+  `0`, so volatility is `0.0` (`constant_series_yields_zero` pins this).
+- **Geometric series.** A constant growth factor produces a *constant*
+  log return; its standard deviation — and so HV — is `0`
+  (`geometric_series_yields_zero` pins this).
+- **Non-positive prices.** A log return is undefined when either price is
+  `<= 0`; that return is treated as `0`.
+- **Non-negative.** Volatility is a standard deviation and is never
+  negative (`output_is_non_negative` pins this).
+- **NaN / infinity inputs.** Non-finite inputs are silently dropped.
+- **Reset.** `hv.reset()` clears the previous price, the window and the
+  running sums.
+
+## Examples
+
+### Rust
+
+```rust
+use wickra::{BatchExt, Indicator, HistoricalVolatility};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // 20-bar window, 252 trading days per year.
+    let mut hv = HistoricalVolatility::new(20, 252)?;
+    let prices: Vec<f64> = (0..40).map(|i| 100.0 * 1.01_f64.powi(i)).collect();
+    let out = hv.batch(&prices);
+    println!("warmup_period = {}", hv.warmup_period());
+    // A perfectly geometric series has constant returns -> zero volatility.
+    println!("last = {:?}", out.last().unwrap());
+    Ok(())
+}
+```
+
+Output:
+
+```
+warmup_period = 21
+last = Some(0.0)
+```
+
+### Python
+
+```python
+import numpy as np
+import wickra as ta
+
+hv = ta.HistoricalVolatility()  # (period=20, trading_periods=252)
+prices = np.full(40, 100.0)  # flat series
+print(hv.batch(prices)[-1])  # no return variation -> 0
+```
+
+Output:
+
+```
+0.0
+```
+
+### Node
+
+```javascript
+const ta = require('wickra');
+// 52 trading periods per year for weekly bars.
+const hv = new ta.HistoricalVolatility(20, 52);
+const prices = Array.from({ length: 60 }, (_, i) => 100 + Math.sin(i * 0.3) * 5);
+console.log('warmupPeriod:', hv.warmupPeriod());
+```
+
+## Interpretation
+
+`HistoricalVolatility` is the realised-volatility number quoted in
+options and risk work — "this stock has been running at 30 % annualised
+vol". Compare it against an option's *implied* volatility to judge whether
+options are cheap or rich, feed it into position-sizing (smaller size as
+HV rises), or track its own trend: volatility clusters, so a rising HV
+tends to keep rising.
+
+Always match `trading_periods` to your bar frequency — annualising daily
+bars with `252`, weekly with `52`, monthly with `12`. Using the wrong
+factor rescales every reading.
+
+## Common pitfalls
+
+- **Mismatched `trading_periods`.** Annualising weekly data with `252`
+  inflates HV by `√(252/52) ≈ 2.2×`.
+- **Confusing it with `StdDev`.** `StdDev` is the population dispersion of
+  *prices*; `HistoricalVolatility` is the sample (`n − 1`) dispersion of
+  *log returns*, annualised.
+
+## References
+
+Historical (realised) volatility is the standard `√252`-annualised
+standard deviation of log returns; the unbiased `n − 1` estimator is the
+conventional choice for volatility estimation.
+
+## See also
+
+- [Indicator-StdDev.md](Indicator-StdDev.md) — population dispersion of
+  raw prices.
+- [Indicator-Natr.md](Indicator-Natr.md) — range-based volatility as a
+  percentage.
+- [Indicators-Overview.md](../../Indicators-Overview.md) — the full taxonomy.
diff --git a/docs/wiki/indicators/volatility/Indicator-Natr.md b/docs/wiki/indicators/volatility/Indicator-Natr.md
new file mode 100644
index 00000000..99bb298c
--- /dev/null
+++ b/docs/wiki/indicators/volatility/Indicator-Natr.md
@@ -0,0 +1,144 @@
+# NATR
+
+> Normalized Average True Range — ATR expressed as a percentage of price, so
+> volatility is comparable across instruments.
+
+## Quick reference
+
+| Field | Value |
+|-------|-------|
+| Family | Volatility |
+| Sub-category | Range-average |
+| Input type | `Candle` (uses `high`, `low`, `close`) |
+| Output type | `f64` |
+| Output range | `[0, ∞)` (percent) |
+| Default parameters | `period = 14` (Python) |
+| Warmup period | `period` |
+| Interpretation | Average true range as a percent of the close. |
+
+## Formula
+
+```
+NATR = 100 · ATR(period) / close
+```
+
+[`Atr`](Indicator-Atr.md) measures volatility in raw price units — a `2.0`
+ATR is large on a $10 stock and tiny on a $5000 index. Dividing by the
+current close converts it to a percentage, so a NATR of `2.0` always
+means "the average true range is 2 % of price". That makes NATR readings
+comparable across a portfolio, and stop or position-size rules expressed
+as a NATR multiple behave consistently regardless of price level.
+
+## Parameters
+
+| Name     | Type    | Default       | Valid range | Description |
+|----------|---------|---------------|-------------|-------------|
+| `period` | `usize` | `14` (Python) | `>= 1`      | Wilder smoothing period of the underlying ATR. `0` errors with `Error::PeriodZero`. |
+
+The Python binding defaults `period` to `14`.
+
+## Inputs / Outputs
+
+From `crates/wickra-core/src/indicators/natr.rs`:
+
+```rust
+impl Indicator for Natr {
+    type Input = Candle;
+    type Output = f64;
+    // update(&mut self, input: Candle) -> Option<f64>
+}
+```
+
+`NATR` is a **candle-input** indicator: it reads `high`, `low` and
+`close`. In Python the streaming `update` accepts a 6-tuple or a dict; the
+batch helper takes `high`, `low`, `close` numpy arrays. Node and WASM
+expose `update(high, low, close)` and `batch(high, low, close)`.
+
+## Warmup
+
+`Natr::new(period).warmup_period() == period` — identical to the
+underlying `Atr`, which is Wilder-seeded over `period` true ranges.
+
+## Edge cases
+
+- **Flat market.** A market with no range has `ATR = 0`, so `NATR = 0`
+  (`flat_market_yields_zero` pins this).
+- **Zero close.** NATR is undefined against a `0.0` close; the indicator
+  reports `0.0` for that bar.
+- **Identity.** NATR equals `100 · ATR / close` bar for bar
+  (`natr_is_atr_over_close_as_percent` pins this).
+- **Reset.** `natr.reset()` clears the underlying ATR.
+
+## Examples
+
+### Rust
+
+```rust
+use wickra::{BatchExt, Candle, Indicator, Natr};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let mut natr = Natr::new(14)?;
+    let candles: Vec<Candle> = (0..40)
+        .map(|i| {
+            let p = 100.0 + f64::from(i);
+            Candle::new(p, p + 2.0, p - 2.0, p, 10.0, i64::from(i)).unwrap()
+        })
+        .collect();
+    let out = natr.batch(&candles);
+    println!("warmup_period = {}", natr.warmup_period());
+    println!("last = {:?}", out.last().unwrap());
+    Ok(())
+}
+```
+
+### Python
+
+```python
+import numpy as np
+import wickra as ta
+
+natr = ta.NATR(14)
+high = np.arange(102.0, 142.0)
+low = high - 4.0
+close = high - 2.0
+print(natr.batch(high, low, close)[-1])
+```
+
+### Node
+
+```javascript
+const ta = require('wickra');
+const natr = new ta.NATR(14);
+const high = Array.from({ length: 40 }, (_, i) => 102 + i);
+const low = high.map((h) => h - 4);
+const close = high.map((h) => h - 2);
+console.log(natr.batch(high, low, close).at(-1));
+```
+
+## Interpretation
+
+`Natr` is the tool of choice whenever an ATR-based rule must work across
+instruments or across long stretches of time where the price level
+drifts. A volatility filter like "skip entries when NATR > 5" or a stop
+at "entry − 3 × NATR %" stays meaningful on any symbol. Use raw
+[`Atr`](Indicator-Atr.md) only when you specifically want the answer in
+price units (e.g. to place a stop a fixed number of points away).
+
+## Common pitfalls
+
+- **Feeding it scalar prices.** It needs `high`/`low`/`close`.
+- **Confusing it with ATR.** NATR is a percentage; an ATR-multiple stop
+  and a NATR-multiple stop are different distances.
+
+## References
+
+NATR is the percentage-normalised ATR as implemented by TA-Lib (`NATR`);
+the underlying ATR is Wilder's from *New Concepts in Technical Trading
+Systems* (1978).
+
+## See also
+
+- [Indicator-Atr.md](Indicator-Atr.md) — the price-unit original.
+- [Indicator-HistoricalVolatility.md](Indicator-HistoricalVolatility.md) —
+  return-based annualised volatility.
+- [Indicators-Overview.md](../../Indicators-Overview.md) — the full taxonomy.
diff --git a/docs/wiki/indicators/volatility/Indicator-StdDev.md b/docs/wiki/indicators/volatility/Indicator-StdDev.md
new file mode 100644
index 00000000..e2f44e3d
--- /dev/null
+++ b/docs/wiki/indicators/volatility/Indicator-StdDev.md
@@ -0,0 +1,156 @@
+# StdDev
+
+> Rolling population standard deviation — the dispersion of the last
+> `period` prices around their mean.
+
+## Quick reference
+
+| Field | Value |
+|-------|-------|
+| Family | Volatility |
+| Sub-category | Dispersion |
+| Input type | `f64` (single close) |
+| Output type | `f64` |
+| Output range | `[0, ∞)` (price-difference scale) |
+| Default parameters | `period = 20` (Python) |
+| Warmup period | `period` |
+| Interpretation | Spread of recent prices; the raw volatility behind Bollinger Bands. |
+
+## Formula
+
+```
+mean     = (1/n) · Σ price
+variance = (1/n) · Σ price² − mean²
+StdDev   = √variance
+```
+
+This is the **population** standard deviation (divisor `n`, not `n − 1`)
+— the exact dispersion measure that drives the band width of
+[`BollingerBands`](Indicator-BollingerBands.md). It is maintained as an
+O(1) state machine: a running sum and a running sum-of-squares, each
+updated by one add and one subtract per bar. Floating-point cancellation
+can leave the computed variance very slightly negative; it is clamped to
+zero before the square root.
+
+## Parameters
+
+| Name     | Type    | Default       | Valid range | Description |
+|----------|---------|---------------|-------------|-------------|
+| `period` | `usize` | `20` (Python) | `>= 1`      | Rolling window length. `0` errors with `Error::PeriodZero`. `period = 1` always yields `0`. |
+
+The Python binding defaults `period` to `20`.
+
+## Inputs / Outputs
+
+From `crates/wickra-core/src/indicators/std_dev.rs`:
+
+```rust
+impl Indicator for StdDev {
+    type Input = f64;
+    type Output = f64;
+    // update(&mut self, input: f64) -> Option<f64>
+}
+```
+
+A single `f64` close in, an `Option<f64>` out. Python maps this to
+`float | None` / `numpy.ndarray` (NaN warmup); Node to `number | null` /
+`Array<number>` (NaN warmup).
+
+## Warmup
+
+`StdDev::new(period).warmup_period() == period`. The first non-`None`
+value is emitted once the window holds `period` prices.
+
+## Edge cases
+
+- **Constant series.** A flat series has zero dispersion, so the output
+  is `0.0` (`constant_series_yields_zero` pins this).
+- **NaN / infinity inputs.** Non-finite inputs are silently dropped; the
+  window and the running sums are left untouched.
+- **Reset.** `sd.reset()` clears the window and both running sums.
+
+## Examples
+
+### Rust
+
+```rust
+use wickra::{BatchExt, Indicator, StdDev};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let mut sd = StdDev::new(3)?;
+    let out: Vec<Option<f64>> = sd.batch(&[2.0, 4.0, 6.0]);
+    println!("{:?}", out);
+    Ok(())
+}
+```
+
+Output:
+
+```
+[None, None, Some(1.6329931618554525)]
+```
+
+The window `[2, 4, 6]` has mean `4` and variance `(4 + 0 + 4) / 3 = 8/3`,
+so the standard deviation is `√(8/3) ≈ 1.633`. This matches the
+`reference_value` test in `crates/wickra-core/src/indicators/std_dev.rs`.
+
+### Python
+
+```python
+import numpy as np
+import wickra as ta
+
+sd = ta.StdDev(3)
+print(sd.batch(np.array([2.0, 4.0, 6.0])))
+```
+
+Output:
+
+```
+[      nan       nan 1.6329932]
+```
+
+### Node
+
+```javascript
+const ta = require('wickra');
+const sd = new ta.StdDev(3);
+console.log(sd.batch([2, 4, 6]));
+```
+
+Output:
+
+```
+[ NaN, NaN, 1.6329931618554525 ]
+```
+
+## Interpretation
+
+`StdDev` is the most direct volatility measure in the library: large
+values mean prices are scattered widely around their mean, small values
+mean a tight, quiet market. Use it on its own as a volatility filter, or
+recognise it as the engine inside `BollingerBands` — multiplying `StdDev`
+by the band multiplier and adding it to an `Sma` reproduces the bands
+exactly.
+
+## Common pitfalls
+
+- **Expecting the sample standard deviation.** `StdDev` divides by `n`,
+  not `n − 1`. For the unbiased return-based estimator use
+  [`HistoricalVolatility`](Indicator-HistoricalVolatility.md).
+- **Comparing across instruments.** The output is in price units; a
+  `StdDev` of `5` is not comparable between a $10 and a $1000 asset.
+
+## References
+
+The population standard deviation is standard statistics; this
+implementation matches the dispersion term of John Bollinger's Bollinger
+Bands and pandas' `rolling(period).std(ddof=0)`.
+
+## See also
+
+- [Indicator-BollingerBands.md](Indicator-BollingerBands.md) — bands built
+  from this dispersion measure.
+- [Indicator-HistoricalVolatility.md](Indicator-HistoricalVolatility.md) —
+  annualised volatility of log returns.
+- [Indicators-Overview.md](../../Indicators-Overview.md) — the full taxonomy.
diff --git a/docs/wiki/indicators/volatility/Indicator-UlcerIndex.md b/docs/wiki/indicators/volatility/Indicator-UlcerIndex.md
new file mode 100644
index 00000000..6d04cf67
--- /dev/null
+++ b/docs/wiki/indicators/volatility/Indicator-UlcerIndex.md
@@ -0,0 +1,161 @@
+# UlcerIndex
+
+> Ulcer Index — Peter Martin's downside-only risk measure: the
+> root-mean-square of recent drawdowns.
+
+## Quick reference
+
+| Field | Value |
+|-------|-------|
+| Family | Volatility |
+| Sub-category | Downside risk |
+| Input type | `f64` (single close) |
+| Output type | `f64` |
+| Output range | `[0, ∞)` (percent) |
+| Default parameters | `period = 14` (Python) |
+| Warmup period | `2·period − 1` |
+| Interpretation | Depth and duration of drawdowns; `0` means no drawdown at all. |
+
+## Formula
+
+```
+max_t       = highest price over the trailing `period` bars
+drawdown_t  = 100 · (price_t − max_t) / max_t
+UlcerIndex  = √( mean( drawdown² over period ) )
+```
+
+Standard deviation treats an up-move and a down-move as equally
+"volatile". The Ulcer Index measures only the **pain of being underwater**:
+for each bar it takes the percentage drop from the trailing high, squares
+it, and reports the root-mean-square. A market that only rises has no
+drawdown and an Ulcer Index of `0`; the deeper and longer the drawdowns,
+the higher the reading. It is the volatility term in the Martin ratio
+(Ulcer Performance Index).
+
+## Parameters
+
+| Name     | Type    | Default       | Valid range | Description |
+|----------|---------|---------------|-------------|-------------|
+| `period` | `usize` | `14` (Python) | `>= 1`      | Look-back for both the trailing high and the RMS window. `0` errors with `Error::PeriodZero`. |
+
+The Python binding defaults `period` to `14`.
+
+## Inputs / Outputs
+
+From `crates/wickra-core/src/indicators/ulcer_index.rs`:
+
+```rust
+impl Indicator for UlcerIndex {
+    type Input = f64;
+    type Output = f64;
+    // update(&mut self, input: f64) -> Option<f64>
+}
+```
+
+A single `f64` close in, an `Option<f64>` out. Python maps this to
+`float | None` / `numpy.ndarray` (NaN warmup); Node to `number | null` /
+`Array<number>` (NaN warmup).
+
+## Warmup
+
+`UlcerIndex::new(period).warmup_period() == 2·period − 1`. The first
+`period` prices fill the trailing-maximum window; the per-bar squared
+drawdown then needs another `period − 1` bars to fill the RMS window.
+
+## Edge cases
+
+- **Pure up-trend.** Price never trades below its own running high, so
+  every drawdown — and the Ulcer Index — is `0`
+  (`pure_uptrend_yields_zero` pins this).
+- **Constant series.** A flat series has no drawdown; the output is `0.0`
+  (`constant_series_yields_zero` pins this).
+- **Non-negative.** The Ulcer Index is an RMS of real numbers and is
+  never negative (`output_is_non_negative` pins this).
+- **NaN / infinity inputs.** Non-finite inputs are silently dropped.
+- **Reset.** `ui.reset()` clears both rolling windows and the sum.
+
+## Examples
+
+### Rust
+
+```rust
+use wickra::{BatchExt, Indicator, UlcerIndex};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let mut ui = UlcerIndex::new(2)?;
+    let out: Vec<Option<f64>> = ui.batch(&[10.0, 8.0, 12.0, 9.0]);
+    println!("{:?}", out);
+    Ok(())
+}
+```
+
+Output:
+
+```
+[None, None, Some(14.142135623730951), Some(17.67766952966369)]
+```
+
+`UlcerIndex(2)` warms up after `3` bars. At bar 3 the squared drawdowns in
+the window are `[400, 0]`, so the index is `√(400/2) = √200`. At bar 4
+they are `[0, 625]`, giving `√(625/2) = √312.5`. This matches the
+`reference_values` test in
+`crates/wickra-core/src/indicators/ulcer_index.rs`.
+
+### Python
+
+```python
+import numpy as np
+import wickra as ta
+
+ui = ta.UlcerIndex(2)
+print(ui.batch(np.array([10.0, 8.0, 12.0, 9.0])))
+```
+
+Output:
+
+```
+[       nan        nan 14.1421356 17.6776695]
+```
+
+### Node
+
+```javascript
+const ta = require('wickra');
+const ui = new ta.UlcerIndex(2);
+console.log(ui.batch([10, 8, 12, 9]));
+```
+
+Output:
+
+```
+[ NaN, NaN, 14.142135623730951, 17.67766952966369 ]
+```
+
+## Interpretation
+
+`UlcerIndex` answers "how uncomfortable has holding this been?" — a high
+reading means deep or prolonged drawdowns, a low reading means a smooth
+ride up. It is most useful for *comparing* instruments or strategies on a
+downside-risk basis, and as the denominator of the Ulcer Performance
+Index (`(return − risk-free) / UlcerIndex`), a Sharpe-ratio analogue that
+penalises only downside volatility.
+
+## Common pitfalls
+
+- **Reading it as two-sided volatility.** The Ulcer Index ignores upside
+  entirely — a wildly choppy *up*-trend can still score near `0`. Use
+  [`StdDev`](Indicator-StdDev.md) for two-sided dispersion.
+- **Forgetting the doubled warmup.** Warmup is `2·period − 1`, not
+  `period`.
+
+## References
+
+Peter Martin and Byron McCann, *The Investor's Guide to Fidelity Funds*
+(1989); the index is also documented at StockCharts. The trailing-high
+drawdown RMS here follows that definition.
+
+## See also
+
+- [Indicator-StdDev.md](Indicator-StdDev.md) — two-sided dispersion.
+- [Indicator-Atr.md](Indicator-Atr.md) — per-bar range volatility.
+- [Indicators-Overview.md](../../Indicators-Overview.md) — the full taxonomy.