Re: Leap Seconds

[Darren New <dnew@san.rr.com>]

Arthur Evans Jr wrote:
> I expect that an Ada program that communicates with an unmanned
> (unpersoned?) space ship might care very much indeed.

Not really. Firstly, I'd be surprised if an uncompensated clock on an
unprotected spaceship actually stayed accurate to a half-second over the
lifetime of its mission. I could be wrong, there.

Leap seconds are really only a problem when calculating intervals
between two declared dates. If you want to know the number of seconds
since some epoch, leap seconds might make a difference. If you want to
know when it's some number of seconds since you launched the spaceship,
the spaceship doesn't need to know about leap seconds, and neither does
ground control if they don't adjust their own clock for leap seconds.

Leap seconds are there to make midnight be "the same time" every day
just like leap days are there to make Jan 1 be the same time every year. 

> Here the problem is not one Ada can solve.  You would need a clock
> at the receiving station that either was never corrected for leap
> seconds, or you would need a table of corrections.

Given clock drift, I don't imagine either of these would be adiquate.

-- 
Darren New / Senior MTS & Free Radical / Invisible Worlds Inc.
       San Diego, CA, USA (PST).  Cryptokeys on demand.
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