Weber fraction: ΔI/I = k; at ΔI=3, I=100 → k=3/100

Sympy-exact witness of the Weber-fraction invariance. Setup: ΔI / I as a two-symbol rational function; Weber's law asserts this is constant (k_w). Identity 1 (symbolic form): 'dI/I' is already the canonical ratio — no simplification…