[LEAPSECS] leap seconds schedule prior to 1972

[Zefram]

John Sauter wrote:
>https://www.systemeyescomputerstore.com/proleptic_UTC.pdf.

Your abstract says you provide a leap schedule for 1900 to 1971, but
actually you provide a leap schedule for -1000 to 1971.  The abstract
seems to suggest some distinction in objective between what is done for
the 20th century and for the preceding 2900 years, aiming to "cover"
the latter but "construct a table of leap seconds" for the former, a
distinction that doesn't seem to make sense and doesn't actually exist
in the paper.  (You do give the leap table in a second format for the
20th century portion, but in substance this is only duplicating part of
the table earlier in the paper.)

Your proleptic leap schedule generally looks sane.  I haven't checked
the numbers in detail.  It is good to incorporate Tony Finch's pUTC, as
you do.  Where more than 12 leaps are required in a year, your extension
to leaping on the 15th day of a month is sensible.

Your delta-T table confuses points in time with the intervals between
them.  The delta-T column itself applies to (the start of?) the specific
year listed, but the "change in delta-T" and "seconds per year" columns
apply to the interval between the year listed on that line and the year
listed on the following line.

The column labelling for that table, and its accompanying text, isn't
great.  You should state what delta-T means, address units, and generally
make clearer what the table means.

You write generally as if UTC exists only for 1972 onwards.  You should
acknowledge the existence of the former (1961 to 1971) rubber-seconds
UTC, and make clear that your schedule is not a proleptic extension of
the whole of UTC but only of the leap-seconds form of UTC.

Your NTP material is mostly a mistake.  For NTP's purpose of clock
synchronisation, it needs to know about contemporary leap seconds, but
has no need for knowledge of historical leap seconds.  There is therefore
no value, for this purpose, in extending the historical leap schedule
further back.  It is entirely erroneous to suppose that this paper has
any bearing on NTP, and I see no value in the paper mentioning NTP.
Some of the specific things you say about NTP are in error, but I won't
go into detail due to this overriding concern.

You should address the question, currently ignored, of what time scale
your proleptic UTC is based on.  If your aim is to fully construct
a time scale, this is a necessary component.  Actual UTC, both of
the leap-seconds form and the rubber-seconds form, is defined as
a transformation of TAI.  TAI is only defined back to some time in
1955, because it is defined by the actual operation of atomic clocks.
This covers Finch's pUTC, but you go far further back, millennia before
there are any atomic clocks.  The delta-T figures that you used are,
strictly, referenced to TT.  To construct a usable time scale you'll need
to use something close to TT as the basis, and manage the transition
between your proleptic basis time scale and the real TAI-based UTC.
I'd be inclined to use the basis TAI(TT) = TT - 32.184 s prior to 1977,
switching to TAI at 1977-01-01T00:00:00 TAI when by definition TAI(TT)
= TAI, though this does mean using a different basis from the real UTC
for five years of real leap-seconds-UTC history.

It would be helpful for you to provide a distinctive name for the time
scale that you construct.  "Proleptic UTC" is a reasonable description,
but not sufficiently specific to use as a name.

-zefram