IV.R427 — m_u/m_d Status Assessment

Light quark ratio remains hardest target. LO: 0.4598 at -29860 ppm (structural, poor precision). NLO: 0.4740 at +29 ppm (precise, ad hoc). Simple: ι_τ(1+ι_τ)=0.4578 at -3877 ppm. Derived sub-5000 ppm formula would promote to τ-effective. p-n formula (IV.T170) provides most τ-native route.