[LEAPSECS] the inception of leap seconds

[Zefram]

Steve Allen wrote:
>https://www.ucolick.org/~sla/leapsecs/leapincept.html

I find it interesting that Time Service Announcement 14 #7
(1970-10-23), explaining the system of leap seconds, explicitly brings
out the similarity between leap seconds and leap days, likening
UTC-with-leap-seconds to a calendar.  This parallel seems to have
subsequently fallen out of pedagogical use, except for the term "leap
second" itself.  The announcement, however, doesn't use the term "leap
second", despite the calendar analogy.  It only refers to the events
as "steps".  Another thing missing from the analogy is the distinction
between arithmetical and observational calendars, which is very relevant,
UTC being observational and the Julian calendar (the announcement's
comparand) being arithmetical.

Time Service Announcement 14 #8 (1971-10-08) discusses the irregular
leap (still called a "step") at the end of 1971, but weirdly gives a
different size for that step from that which is implied by tai-utc.dat.
The announcement states a step size of 107600 us, but the expressions in
tai-utc.dat imply a step size of exactly 107758 us.  The announcement is
ambiguous as to whether this step size is specified in microseconds of UTC
or of TAI, apparently ignoring the UTC frequency offset for this purpose,
though the offset isn't anywhere near big enough to account for the
discrepancy.  The 107758 us computed from tai-utc.dat is in microseconds
of TAI, and the leap is only a few nanoseconds shorter in UTC.

-zefram