Representative dispersion corrected δOPD^meas time series for the A–B configuration on MJD = 60918 with A in MIRC-X and B in MYSTIC (MYSTIC DDLs shown). Blue points show the measured δOPD^meas (W2 reference) for the six baselines; the orange lines show the geometric model δOPD_geo(t) = B(t) · (r_A − r_B) computed from the time-varying (u, v) and the A–B astrometry. The slow drift follows the changing projected baseline with hour angle, while baseline-dependent offsets between data and model indicate residual H–K dispersion and non-common-path terms. Per-scan scatter is at the 3–4 μm level, but our astrometric OPD uses time-averaged DDL positions and fringe tracking residuals, reducing the effective noise to ∼0.37 μm.