EW equation: ∂h/∂t = ν∇²h + η. KPZ adds nonlinear term: ∂h/∂t = ν∇²h + (λ/2)(∇h)² + η. In 1D: EW has β=1/4, KPZ has β=1/3 roughening exponent for width W(t)~t^β.