On Sat 2022-07-30T13:24:01-0400 Brooks Harris hath writ:
On 2022-07-30 1:01 PM, Paul Eggert via tz wrote:
Given the other comments in this thread I'm inclined to revert the effect of this change, so that vanguard form continues to use integer multiples of a second. So I installed the attached further patches, the last of which does the reversion. I think that's best for civil time. But I had a thought. Steve Allen seemed to like the idea and I'm sympathetic to his needs as astronomer. Maybe subsecond precision could be added to "right" instead of vanguard?
No, tz does not need subsecond precision, not for anyone, not in any era. The French law of 9m 21s is an example. The legislators should have known about the funds which had been expended as part of the two century effort to establish the offset between Greenwich and Paris, and that the disagreements of many 0.1 s in their own lifetimes were from the techniques employed by the astronomers, not from the telegraphs or radios. The sub-second astronomical offsets all date from before the 1970 cutoff. 1970 was when the CCIR was persuaded to assert that one second is close enough for everyone. Historically the best time comparisons had poor precision. Before the 20th century offsets were many 0.1 s or even > 1 s. In the early 20th century offsets were still many 0.01 s or even > 1 s. Attempts to reach a precision of 0.0001 s were not widespread until the International Geophysical Year of 1957/1958. Offsets of many 0.001 s persisted after the adoption of the cesium-based coordinated time because the Soviets used their own coordination scheme and other countries did not convert from UT2 to coordinated cesium time until the late 1960s. tz has rightfully eschewed the notion of trying to track local offsets recorded in Bulletin Horaire and Circular T. The legal time of the US was offset by 0.035 seconds from the BIH at 1958-01-01. The USNO and US NBS did not attempt to bring their time scales into microsecond agreement until 1968. Over a long interval in this century the legal time of Hungary was 50 microseconds different from UTC in most other places because the time lab there declined to perform a reset of their cesium. Thinking of encoding these things is a world of pain that tz does not need. -- 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