What time is it?
 

Here is one of those very annoying questions that you might like to see if you know the answer to. I didn’t and was fascinated to read an article on the subject last night.

I always thought the clock on my GPS was accurate and occasionally set my wrist watch using it. I gather this is not strictly correct but why not!

Go on tell us!!

I too believed gps time was accurate! Let me know the truth ;)

Believe it or not, there is more than one time.

See http://tycho.usno.navy.mil/systime.html for some well(?) known ones.

To make it even more interesting, there can be differences between them.

This is mainly due to 'leap seconds' - basically a tweak every 6 months or so, to help syncronise times between the systems.

So as of 1 January 1999,
International Atomic Clock is ahead of UTC by 32 seconds.
GPS is ahead of UTC by 13 seconds.

At least thats my argument when Mrs Seat Of My Pants says "You promised to be home at 10:30" - Ah but which time system?

Seat of My Pants - you are spot on and very well informed.

I came across this in a very good article in New Scientist this week. GPS time is indeed "wrong" by 13 seconds. There is also a slight worry that at 1 sce past midnight soon GPS time will find an extra day on some receivers and then lose the day again.

That's true, but has nothing to do with the clock displayed on your GPS receiver! The receiver, at least if it's any of the standard ones from Garmin etc., knows about the difference and displays UTC, not GPS time.