A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Peter Monta
Date: 2018 Nov 6, 13:17 -0800
However, nowadays the polar motion is predicted and published a year in advance in IERS Bulletin A to .001″ precision. Bulletin B has more accurate values determined after the fact.
The uncertainty of the pole a year in advance is quite a bit larger than 1 mas, though. Bulletin A says the uncertainty is already 13 mas for 40 days out, and gives a little power-law formula that gives 75 mas for a year out. But yes, the measured values are good to 90 uas (~3 mm).