Millimeter-level GCRS→BCRS→GCRS frame-closure test of the BCRS implementation in JPL GipsyX. Panels show radial/along-track/cross-track residuals Δr(T) (m; note the 10⁻³ scale) over 24 hr. The test uses DE440 (TDB argument) and identical force models in both runs (Table 6); states are mapped using the screened operational transformations Equations (36), (42), (51).