On 1/20/2015 6:14 PM, Jochen Bern wrote:
So, what*function* might people be thinking of when they assert those
properties to apply (or not) to timescales?
TAI = UTC(x) and UTC = TAI(x). And that's part of the problem.
There seems to be the thought that if you do that across a leap second,
and use a UTC time series (or timestamps, if that makes it more clear),
but use a TAI-like scale, there will be discontinuities on the graph,
where points (23:59:60) can't be plotted (or the other way, where points
make stepwise jumps).
But of course, that's wrong, because both scales increase linearly, and
there is no discontinuity in either. Both account for every bit of time
- linearly, continuously, and monotonically (UTC+x = time+x, if you
will). Time+1 in one simply maps to time+1 in the other. The only change
is to what that value is called, not the value itself.
The real problem is systems (POSIX, particularly), which incorrectly
handle time, despite having over 40 years to get it right. They try to
please everyone, while pleasing no one. POSIX tracks and does
calculations on determinate intervals (seconds since 1/1/1970, and every
minute has 60 seconds), and also tries to handle civil time, which has
indeterminate intervals (unpredictable 61 second minutes). So it fails
by trying to do two mutually exclusive things.
It's not a particularly difficult problem to solve (timezone info is
regularly updated because of civil changes, historical leap seconds
could be, too), but requires thought about whether specific future
events should be considered as intervals or absolute time values.
(Also, in English, it's "monotonic," not "monotonous". "Monotonous"
means uninteresting or boring, which this likely is)
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