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Bob,

There are only a couple ways to pick up that suspected sudden 2 second time jump. By short wave time ticks or by comparing to a rated quartz watch. I have a Citizen quartz watch which losses less than a second per month that is capable of picking up a sudden 2 second discrepancy. There is no way that sextant CN observations could show a 2 second time shift vs. GPS. Index error uncertainty alone would mask such a small change. Then there are many other uncertainties: Height of eye, sextant perpendicularity to horizon, horizon quality, temperature & pressure deviations from mean, sextant temperature, shade combinations, back lash of micrometer drum, to name a few. If the sextant observations were made from a sailboat cockpit then intercepts of +/- 3' would be considered good which translates to +/- 12 seconds of time on a prime vertical observation. It would take a time shift of at least 20 seconds to get noticed I would think.

Greg Rudzinski 

From: Bob Goethe
Date: 2015 Sep 8, 20:48 -0700

I had an odd experience last summer.  I was on a boat for 19 days, doing celestial for many of them.  I had rated my Casio Wave-Ceptor watch before leaving home, and so knew what its typical rate of gain/loss was when out of range of the NIST transmissions.

Both I and the boat's captain (who also was doing some sextant work) felt like we noticed two occasions when the GPS clock jumped ahead by a couple of seconds on a given day, and then fell back to what we expected the following day.

I was not listening to WWV on the shortwave, so I never got a golden-standard for my time observations.  All I had was a vague sense that the time on the GPS receiver was maybe not reliable.  Has anybody else noted something like this...or did I simply make a couple of spurious observations?

Bob