Zhou chaotic system — dx/dt = a·x + y·z, dy/dt = b·x + c·y − x·z, dz/dt = −d·z + x·y with c=−1 d=2.5 fixed. Classic a=−10 b=40. Dual a+b sliders. Distinct from chen-celikovsky.html, chen.html, chen-lee.html, lu.html, rayleigh-benard.html (Shimizu–Morioka). Bulk centroid ≈ (-0.0088, -0.0039, 25.8035). RK4 Zhou fold. Gold low-alpha trail, cap 650. RM = settled silhouette, no animate-on.