IV.T193 — Bottom Mass from τ-Chain at −1351 ppm

m_b = (17/20)·ι_τ^(-20/13)·m_n = 4174.4 MeV at −1351 ppm from PDG 4180±7 MeV (0.8σ). Combined exponent −20/13 = −lobes²·W₃(4)/a₃ = −4×5/13. Standalone formula combining top prefactor with ratio exponent.