On Mon, 10 Nov 2003 16:06:42 -0500, M. Adam Davis wrote:

> My atomic clocks set themselves according to DST just fine.  They have
> the Time Zone switch on the back, and then an additional DST switch.
>
> Unfortunately, one of them checks the time signal at 11pm, which is
> before the 2am DST change, and it didn't change until I pressed the
> 'wave' button, which forces a time check.  Took a few seconds to change.
>
> The other one did just fine.  I assume it resynchronizes after the 2am
> time change.  The DST bit is sent along witht he transmission, so the
> clocks don't have to do any real computing...

Indeed, they can't, because the rules change from time to time.  Only a few years ago the UK used to change at
02:00 and 03:00 local, then we fell in with Europe and now change at 01:00 GMT.  There is a bit sent with the
MFT signal which means "Change Pending" for about a day before the change, which alerts clocks to look more
often then usual to see when the change occurs - some clocks only resynchronise with the radio signal every
few hours (once a day in some cases) so they step up to checking  hourly when a change is pending.  Of course,
that's the intention - there's nothing to say that every clock designer actually includes this feature!

Cheers,

Howard Winter

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