Description: This paper derives the proton/electron mass ratio, m_p/m_e = 6π⁵ = 1836.118 (measured: 1836.153; discrepancy −0.002%), from a single geometric postulate added to General Relativity. Beginning from the Einstein field equations restricted to static spherical symmetry, we adjoin a positional time-dilation postulate — the structural completion of the special- and general-relativistic derivative hierarchy by its zeroth-order term — and show that the spacetime metric is then fixed uniquel