On Jan 14, 2011, at 4:39 PM, Joe Gwinn wrote:
> At 3:03 PM -0700 1/14/11, Rob Seaman wrote:
>
>> If you wish. In that case, note that sexagesimal notation is used for
>> angles, while systems like Unix often express "measurements of time"
>> intervals as unending counts of seconds (SI or otherwise) since some epoch.
>> That epoch, eg midnight 1 Jan 1970, was itself selected as representing an
>> angle related to the Earth.
>
> In any event, POSIX time is not an argument for or against any of the debated
> leapsecond proposals.
Glad to hear it, which is why I didn't say anything about POSIX, but rather
"systems like Unix".
Angles repeat every 360 degrees or 24 hours. Sexagesimal repeats every 24
hours or 86400 seconds. Angles may also be defined as being positive definite.
The representation should match the nature of the quantity involved.
Timing intervals on the other hand are open-ended, an endless count perhaps
extending negative as well as positive. Issues like overflowing a POSIX
defined buffer are implementation details. In principle, intervals map to the
entire real number line.
There are any number of ways a "clock" could be constructed, for examples:
http://www.ucolick.org/~sla/navyls/0716.html
UTC, however, is the underlying clock for civil timekeeping and should be
responsive to civil timekeeping requirements. The most evident of these is the
ubiquity of the synodic day as the primary cadence of our lives.
As PHK says: "both are needed, for sure..."
> In any event, POSIX time is not an argument for or against any of the debated
> leapsecond proposals.
There are no "leapsecond proposals", only the single ITU draft seeking to
redefine UTC. Focusing on leap seconds obscures the real issue. Leap seconds
have only ever been a means to an end. Our discussions (not "debates" since
there has only ever been one option on the table) - our discussions have often
confused the ends with the means.
Rob
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