A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2015 May 31, 21:27 -0700
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.
I've been working 2nd shift lately and I sleep during the morning hours. Also, the moon was not full on either date, so I used the "not-so-preferred" method of superimposing the direct and reflected images of the moon to determine index error. (As opposed to limb-to-limb contacts.) Therefore, the index error might well be -0.4'.
Regarding your questions:
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?
I was using the 3.5x scope that came with the sextant. (I've been meaning to get a 7x. But, after the bills, I never seem to have any money to play with.) At first, I was just trying to get Jupiter to just brush the limb of the moon. About halfway through the round, I decided to try and 'split' the planet with the moon's limb. This may explain the apparent improvement midway through the round. But, as I have alluded to before, I have a problem holding the sextant steady for any amount of time beyond a few seconds. I think this is due to a slight tremor I have when trying to hold something really steady. (The same thing happens to me occasionally at the shooting range. (!) ) So, I was also consciously trying to complete the shots quicker, too. I have to wonder if a 7x scope might exacerbate the problem. I really should try some exercises to help steady my hands, as some NavList members have suggested.
As for the "max. error in long.", those figures are simply what my error would have been if I had only used the single "worst" sight from each round. (Same goes for the "minimum".) If I were actually using the data to navigate, I would probably graph the results, draw a line through the "middle" of the rest, discard the outliers and use the data from one of the shots closest to the line. (Is that even the best way to go about it?) I must admit, I know almost nothing about statistics, and am slightly confused about how the maximum error would've risen with more sights. Unless it's statistically probable that, with more sights, I'm more likely to get some really bad ones. Thanks for the feedback, and thanks in advance for any advice on statistical analysis, as well.