time for time details

[Moderator, John Quarterman]

From: ames!pyramid!nsc!nscpdc!nscpdc.nsc.com!djg
Date: Sun, 28 Dec 86 11:47:06 pst

> From: seismo!nbires!vianet!devine (Bob Devine)
> Date: Wed, 17 Dec 86 19:39:53 EST
> 
>   This is in response to Ron Tolley's article that appeared in mod.std.unix
> last week.  My reply corrects the errors.
.....
> > solar time.  Note that with  Greewich Mean Time, such  corrections  were
> > made  by  stretching  or  contracting  the  length  of  seconds.  UTC is
> > generally available through time standards, GMT not readily available.
....
>   A second is not stretched/contracted for leap second adjustments.  The
> selected minute will have 59 or 61 seconds.

Note as above it was G.M.T that was stretched.
I used to work at the R.G.O. Whenever possible a zenith tube reading of
Polaris was used (up to the installation of caesium clocks 20? years ago)
to correct an oscillator defining a 10MHz signal sent via land line the
Rugby time centre for broadcast. On every hour the signal was inverted 
5 seconds before the hour to synchronise clocks (This is still done but from
atomic clocks). Since using U.T.C the leap seconds are manually added or
subracted at the appropriate time (Yes someone at midnight dec 31 has to go
down to the time computer and press a button).
Note that since UTC is the calculated best fit of many atomic clocks
it can never be given in "real time" but only after the fact.
(Most laborities(observatories) use quartz clocks set against a reference
and then post-calibrate it).

Volume-Number: Volume 9, Number 9