# Re: [LEAPSECS] how do computer people want their time clocked?

From: Deckers, Michael <Michael.Deckers_at_fujitsu-siemens.com>
Date: Wed, 30 May 2001 15:45:29 +0200

On 2001-05-30, Garrett Wollman wrote thusly:
>
> The requirement that I've heard most commonly is much simpler: there
> must be 86,400 nominal seconds per nominal day, .....................
>
I also often hear similar arguments, and try to respond like this:

-- "But there are _86 400_ seconds in a day -- if you set back a clock
by a second (as is done with UTC every once in a while) you do not
change the number of seconds in a day. You adjust the clock, not the
time units."

-- "Then to which day does a leap second in UTC belong?"

-- "By UTC convention, the adjustment happens at the end of a calendar day,
just before midnight. Upon reaching 24:00:00 that day, UTC is set
back by 1 s, effectively running again from 23:59:59 to 24:00:00."

-- "But then the true elapsed time between 23:59:58 and 00:00:01 is 4 s,
and you actually _do_ have a day with 86 401 s."

-- "No -- what you mean by 'true elapsed time' is the difference between
the readings of TAI at the two instants. The readings of TAI at
the 2 instants are in fact 00:00:29 and 00:00:33, a difference of 4 s.
The readings of UTC are only 3 s apart. Since UTC is slower than TAI,
the differences between the readings of TAI and UTC just cannot always
be the same."

And thus it can go on for some time, arguing that the leap second actually
is from 23:59:59 until 23:59:60, questioning what true time actually is, etc.
It is from such dicussions that I got the impression that monotonicity
is all they need.

> ............................................... and nominal days must
> be the same ordinal and duration as provided by local law and custom.

This is in fact a good argument for most countries. I seem to recall,
though, that some countries officially still use mean solar time
(even the UK legally use GMT).

Michael
Received on Wed May 30 2001 - 06:48:16 PDT

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