A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 May 31, 12:01 -0700
Thanks for posting that data. Those look like very good results. The standard deviation is about 0.45 minutes of arc for the whole bunch, and the average error is -0.4 minutes of arc. I would suggest that you have refined your index correction here. That's what the average error is telling you. Instead of +0.8', you should perhaps use +0.4' for your IC. On the other hand, this observation of lunars with Jupiter, and Saturn, too, is slightly sensitive to the way you make contact with the Moon's limb. Were you splitting the disk of Jupiter on the limb (that's recommended)? Also, could you tell us what scope you were using on your sextant? With a 7x scope, I get about a quarter of a minute of arc standard deviation, but if you were using a 3.5x scope, then your results are basically the same as mine (or slightly better!).
I have one "complaint" on the way you've summarized your results. You've included a "max. error in long." number. This is statistically irrelevant. This number will necessarily rise with more sights taken while the accuracy of your result actually improves (down to the limit of systematic error, including whatever error there may be in the index correction). The "maximum error" tells us nothing useful, and worse, it can easily mislead.
Conanicut Island USA