[ntp:questions] Re: GMT: UT1 vs UTC

Tom Van Baak tvb at leapsecond.com
Sun Nov 2 23:33:51 UTC 2003

"David L. Mills" <mills at udel.edu> wrote:

> If we ever had to give back a leapsecond, it would be a disaster. The
> WWV/WWVB timecode has only a single bit to signal leap insertion and no
> way to signal deletion. The GPS timecode has the UTC-GPS offset in


Not true. Yes, there is only a single bit in the
WWV/WWVB timecode to indicate a pending
leap second but the sign and magnitude of the
UT1 correction bits tell you if the leap second is
positive or negative. For WWVB these are bits
36/37/38 for the sign and bits 40/41/42/43 for
the magnitude.

For example, for the 6/30/1997 leap second the
UT1 correction was -0.5 before the leap second
and +0.5 after the leap second. Similarly for the
12/31//1998 leap second the UT1 correction was
-0.3 before and +0.7 after the leap second.

When the net change in UT1 correction is +1.0
the leap second will be positive and if the net
change is -1.0 it will be a negative leap second.
So a separate bit for positive/negative leap second
is not needed in the specification.

I'm not saying there won't be hardware or software
trouble elsewhere if a negative leap second were
ever to occur, but the WWV/WWVB time code
specification itself is not a limitation.

For details on the leap second examples above see:



More information about the questions mailing list