https://en.wikipedia.org/wiki/Prime_meridian_(Greenwich) https://en.wikipedia.org/wiki/Prime_meridian_(Greenwich) > The actual reason for the discrepancy is th

https://en.wikipedia.org/wiki/Prime_meridian_(Greenwich) https://en.wikipedia.org/wiki/Prime_meridian_(Greenwich) > The actual reason for the discrepancy is that the difference between precise GNSS coordinates and astronomically determined coordinates everywhere remains a localized gravity effect due to vertical deflection; thus, no systematic rotation of global longitudes occurred between the former astronomical system and the current geodetic system. Cites https://link.springer.com/article/10.1007/s00190-015-0844-y https://link.springer.com/article/10.1007/s00190-015-0844-y which breaks down the reason for the approximately 102 m difference ("In Sects. 2 and 3, the authors show that the deflection of the vertical (DoV) can account for the entire longitude shift at Greenwich.") and some of the alternatives. For example: > Crustal motion from plate tectonics is also much too small to explain the observed longitude difference. Britain and most of Europe are moving toward the northeast at about 3 cm/year (a longitude change of 0.1 arc-second/century) with respect to the WGS 84 terrestrial coordinate frame (Altamimi et al. 2012). The accumulated effect relative to other monitoring stations amounts to only a few meters since its designation as prime meridian in 1884.