NavList:

Doug, the following information may be encouraging.

Close, in his "Text Book of Topographical and Geographical Surveying", London 1905, writes on page 202 and 203:

"... note carefully the sidereal times to the nearest tenth of a second of the transits of star and bright limb of the moon over each wire."

and further on "... an error of a second of time produces about 30 second's error in the longitude. We may assume in the ordinary case an error of ⅓ second and a resulting error of 10 seconds of longitude. As a rule, only about eight observations can be taken in a month, so after a month's work the mean of the results would be about 3 or 4 seconds in error, or say nearly 1 minute of arc."

I guess you don't have a watch running sidereal time, and you don't need one either. With the method I described your watch should run mean (solar) time. For short time intervals the difference between sidereal and mean time is however very small. Good luck with your observations.

Lars