In <199610032320.QAA04986@shade.twinsun.com>, Paul Eggert <eggert@twinsun.com> said:
I also used to believe that UTC was established in 1972, but I've been corrected. UTC was introduced in 1961. It was originally kept close to UT1 by periodically adding or subtracting steps of a fraction of a second. 1972 is when the current leap-second regime was instituted.
Hmmm, so POSIX's epoch *is* well defined then. Do you know if there are any records of when and by how much the various UTC adjustments were made, particularly for the interval 1970-01-01T00:00:00 until the first leap second (1972-06-30T23:59:60)? I'm interested in revisting the issue wollman@uvm-gen.EMBA.UVM.EDU raised in <9402062245.AA18471@bajoran.emba.uvm.edu>:
...According to the bulletins that I've seen, |TAI-UTC| is about 28 seconds now. However, the leapseconds file only lists 19 steps. This is probably due to the fact that the first step was 10 seconds, not just 1. Is there an easy way to fix this, so my users who use NTP don't complain about their clocks being nine seconds off?
[Note to new readers: this is somewhat misleading. The "first step" of 10 seconds was actually the defintion that UTC-TAI would be exactly 10s when the new leap second mechanism was introduced. This was because UT1-TAI was about 10s at the time and UTC had been tracking UT1 and so was therefore also about 10s off of TAI at that time. Any actual stepping (or leaping) involved was of a fraction-of-a-second nature.] Given the "UTC established 1972" misunderstanding at the time, this was considered an awkward problem to address. But it sounds like it may actually be possible to invent some "phantom leap seconds" which are backed up by some version of "truth" in an implementation of the suggestion made by Paul Eggert in <9402072149.AA05650@spot.twinsun.com>:
B. Invent some leap seconds for the period between 1970 and 1972, as if UTC had been in effect then. This lies about UTC but repairs the 2 or 3 s error. The conversion correction would be correspondingly reduced, to 7 or 8 s.
Provided, hat is, that someone can find records of how UTC was kept almost-in-sync with UT1 prior to 1972. --Ken Pizzini (NB: referenced articles are in the tzarchive file on elsie).