On 2022-10-04 5:20 PM, Paul Eggert via tz wrote:
Predicting length of day (LOD) is a tricky business with no real consensus.
I think that statement is a little misleading. While there is no specification for, that is, there no "official product" of, C04, it is internally used by both the USNO, as the timescale maintained, distributed to, and used by GPS, and the IERS, to determine values published in Bulletin A and to determine leap-second values as published in Bulletin C. From what I can tell C04 is *the* 'consensus' of LOD as a matter of practical common use. # EARTH ORIENTATION PARAMETER (EOP) PRODUCT CENTER CENTER (PARIS OBSERVATORY) - INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE # EOP (IERS) 20 C04 TIME SERIES consistent with ITRF 2020 - sampled at 0h UTC https://hpiers.obspm.fr/iers/eop/eopc04_20/eopc04.1962-now (This is the version distributed by the IERS. (There are other links at USNO and NIST, and possibly others, to the same information) It is indeed very tricky business, but the good folks at the many contributing observatories and time laboratories together with many data processing centers have made landing an airplane within a few inches possible. How this is accomplished is a topic of a very long essay. -Brooks