// Licensed under the Apache License, Version 2.0
// © mihakralj
//@version=6
indicator("First Derivative / Velocity (SLOPE)", "SLOPE", overlay=false, precision=8)

//@function Calculates the first finite difference (velocity): Slope = V[t] - V[t-1]
//@param src Source series
//@returns First difference of consecutive values. Returns 0.0 on first bar.
//@optimized Uses direct history access for zero-allocation streaming.
slope(series float src) =>
    float prev = src[1]
    if na(prev)
        0.0
    else
        src - prev

// ---------- Main loop ----------

// Inputs
i_source = input.source(close, "Source")

// Calculation
s = slope(i_source)

// Plot
plot(s, "Slope", color=color.yellow, linewidth=2)