IV.R127 — All roads lead through m_e

Every atomic-scale prediction factors through m_e = m_n/R(iota_tau): a_0 ~ 1/m_e, E_1 ~ m_e, R_infinity ~ m_e, lambda ~ 1/m_e; the 0.025 ppm precision of m_e is the ceiling for all atomic predictions, improvable only through Level 2 mass ratio corrections or better neutron mass measurements.