Re: [LEAPSECS] consumer-quality clocks

From: Brian Garrett <>
Date: Sun, 1 Oct 2000 23:02:34 -0700

----- Original Message -----
From: Joseph S. Myers <jsm28_at_CAM.AC.UK>
Sent: Sunday, October 01, 2000 1:04 PM
Subject: Re: [LEAPSECS] consumer-quality clocks

> Does anyone here know of consumer GPS receivers (as opposed to ones
> intended for precise time synchronisation) that provide for display or
> readout of both the current and future leap second offset data from the
> GPS signals? When I asked about this on the tz list a while back Meinberg
> receivers and others designed for time synchronisation were mentioned, but
> not any of the consumer GPS receivers. (Ideally I'd want both display and
> readout of UTC, including 23:59:60; TAI; and the past and future leap
> second offsets and effectivity times. The customer enquiries email
> addresses and web forms of companies making consumer GPS receivers don't
> seem to respond to enquiries that carefully reference the parameters from
> the GPS Standard Positioning Service Signal Specification that are of
> interest.)

As far as I know, most consumer-grade GPS units can display the user's local
time zone, UTC or GPS time. I suppose some might be able to display TAI,
but since the majority of those users purchasing the lower-cost units have
little or no reason to care about TAI, the manufacturers seem to have
ignored it. For the same reason, leap-second data seems to have been
ignored as well. (Future leap-second data probably wouldn't be available in
any case, given that they are announced ad-hoc by the IERS and the leap
second "warnings" areonly inserted into GPS satellite broadcasts a few weeks
in advance.)

As for how GPS readouts handle the leap second itself, the answer seems to
be: somewhat erraticaly.
I've not owned my Magellan 315 long enough to see what it does with one, but
I seriously doubt it would do 23:59:60 (or 3:59:60 PM if I still had it on
Pacific time). The NMEA output from any GPS should indicate a leap second
as it occurs, but exactly how it is handled seems to vary with the receiver.
For examples from the 1997-06-30 leap second event, see .

Hope this helps,
Received on Sun Oct 01 2000 - 23:02:30 PDT

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