[android-developers] Re: How to store date and time in database

I didn't realize until now that POSIX absolutely FAILED on this. Every
description I've seen of this time indicates either that it's number
of seconds since January 1, 1970, or that it's UTC -- but it is, in
fact, neither.

((Bangs head on keyboard at one second intervals, carefully skipping
over leap seconds)).

I'm torn between thanking you for pointing this out, and screaming!
Both, I guess. I guess it shows how poorly people -- even people on
standards committees who OUGHT to know better -- understand time.

See the Sun Javadoc for the wiggle room Java allows, based on whatever
imperfections the underlying OS has on this score:
http://download.oracle.com/javase/6/docs/api/java/util/Date.html

The Android SDK documentation, on the other hand, is pathetically
silent on the matter.

The Wikipedia article on Unix time indicates that there's discussion
of dropping leap seconds, and letting civil time drift. I guess
eventually, "noon" will lose whatever vestiges of meaning it has now.

This has been a sore point for me for decades. Timekeeping with
sufficient accuracy (i.e within seconds) for celestial navigation is
one of the greatest scientific endeavors, occupying some of science's
best minds over centuries, culminating in the Longitude Prize, offered
in 1714 and ultimately won in 1773.

The earth rotates one nautical mile at the equator every 4 seconds, so
even one second of error in time contributes significant error in
position.

I have in my possession the 6 volumes of Sight Reduction Tables
published by the US Defense Mapping Agency. 6 volumes of tables of
numbers for accurate calculation of spherical trigonometry with
detailed attention to accuracy, carefully described procedures for
calculation, down the the model of computer (IBM 1401) used to perform
the calculations. And yes, I used to use them. When your personal
safety, and of your crew, depends on accurate time, it gives you a
different perspective on the matter!

Accurate timekeeping is no less important in computer systems, where
properly sequencing internal and external events is often critical --
and sometimes involves life safety. Yet generations of programmers and
system administrators alike have refused to be bothered with accurate
timekeeping.

I guess I'll go protest by setting all my clocks to UTC. (I've used
exclusively 24-hour time for almost 40 years, and am used to doing the
conversion to/from UTC, so it won't bother me!)

On Dec 27, 9:12 pm, Steve Allen <sla29...@gmail.com> wrote:
> On Dec 26, 11:39 pm, Kostya Vasilyev <kmans...@gmail.com> wrote:
>
> > With all due respect, there is a much easier way.
>
> > Java date/time stamps are internally represented by "long" values, the
> > value being the number of milliseconds since Jan. 1, 1970 GMT.
>
> Keep in mind that the count of milliseconds does not conform to
> legal nor physical elapsed time for any observer.  See here for morehttp://www.ucolick.org/~sla/leapsecs/epochtime.html

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