[LEAPSECS] Java JSR-310 TAIInstant class

Stephen Colebourne scolebourne at joda.org
Sat Jan 29 17:21:10 EST 2011

On 29 January 2011 17:35, Steve Allen <sla at ucolick.org> wrote:

> On 2011 Jan 29, at 09:23, Warner Losh wrote:

>> A second minor point: TAI does not exist before this point.  Proleptic TAI is used, but more often TT is used for epochs prior to the present.  I'd just note here that a proleptic TAI is used for dates prior to the 1958 epoch.


> The agreement to synchronize on UT2 as of 1958-01-01 was not made

> until 1959, so TAI did not really exist at that point either.  If

> extrapolation is allowed then the BIH records can take TAI back

> to mid 1955 when the UK time broadcasts started being compared

> with the first cesium chronometer.  And none of this makes sense

> to include in a generic API, for the table lookups necessary to

> implement it are painstaking.

I'll happily concede that TAI did not exist prior to x, where x might
be 1972, 1958, 1959 or some other date. Frankly, that isn't very
important to the API IMO. If someone with that much knowledge of the
history of time-scales wants an "accurate" instant for some far past
date then thats their problem and they can't expect JSR-310 to help.

What JSR-310 needs is a single time-scale that has a single
incrementing number of fixed size units (SI seconds) with no other
interpretations (such as what a day is). I believe that TAI best meets
that definition today, and thus is the choice made.

I can and will clarify that it has less meaning (as TAI or otherwise)
when viewed proleptically back into history.

@Warner, I'll also rephrase the point about GPS being easy to access.


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