On Thu 2020-11-12T12:11:52-0700 Paul Gilmartin via tz hath writ:
Was UTC defined in 1970, or should it pedantically be GMT for 1970 and 1971; TAI-10 thereafter?
Pedantically there are no answers which are universally true. During 1970 and 1971 (and a few years before) different time service bureaus were providing various different time scales with various different names in their radio broadcast time signals. US NBS provided two different broadcasts with different time scales (old UTC and stepped atomic time SAT). German PTB provided two different time scales at different times of day using the same transmitter (old UTC until that became illegal in Germany, thereafter SAT). During those years the terminology UTC was only known inside the time service service bureaus. As for GMT, the final observation using the Greenwich meridian circle was 1954-03-30. After that date there was no authority who could provide a definition of GMT. The last use of that term by almanacs was in 1959. The term GMT continued to be used by some time service bureaus, but in accord with CCIR recommendation 374 they were broadcasting the original form of what was internally known as UTC. On 1974-01-01 NBS WWV stations started announcing as UTC. In 1976 the IAU urged no further use of GMT. In 1978 the CCIR was informed that GMT was no longer used. In 1980 the CCITT specified UTC to replace GMT for all telecommunications activities. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m