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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Fleming
Date: 2015 Jun 23, 16:19 -0700
| IC measurements | 06/05/15 | ||||||||
| overlap | edge to | edge | difference | sum | |||||
| 1 | 3.2 | on | on | 32.6 | 28.3 | off | 4.3 | 60.9 | |
| 2 | 3.5 | 31.6 | 28.6 | 3 | 60.2 | ||||
| 3 | 4.2 | 32.2 | 29 | 3.2 | 61.2 | ||||
| 4 | 3.3 | 32 | 29.3 | 2.7 | 61.3 | ||||
| 5 | 3.9 | 32.6 | 29.1 | 3.5 | 61.7 | ||||
| 6 | 3.2 | 32 | 28.6 | 3.4 | 60.6 | ||||
| 7 | 4.1 | 32.4 | 29.1 | 3.3 | 61.5 | ||||
| 8 | 3.8 | 32 | 29.4 | 2.6 | 61.4 | ||||
| 9 | 3.1 | 31.8 | 30.1 | 1.7 | 61.9 | ||||
| 10 | 3.5 | 32.1 | 29.2 | 2.9 | 61.3 | ||||
| 11 | 3.4 | 32.5 | 28.9 | 3.6 | 61.4 | ||||
| avg | 3.56 | 32.16 | 29.05 | 3.11 | 61.22 | Sum/4 | |||
| std | 0.38 | 0.33 | 0.48 | 0.66 | 0.49 | 15.30 | |||
| Semidiameter | 15.8 |
| |||||||
Fred Hebard claimed that edge to edge sun index measuremets were more accurate than overlapping measurements. I don't believe the above data supports that claim.
Two sets of measurements were made on my Astra sextant with the 3.5 power scope. First column is 11 overlapping measurements with about 1/10 sun diameter side error which I believe is helpful for overlap judgement but no proof for that.
Then the side error was removed and I made 11 edge to edge measurements (22 measurements in all).
Precision in all sets of primary measurements are reasonably identical order of .4 moa.
But we see that the precision of the edge to edge values shows higher spread, .66 moa. Taking the difference of two numbers increases their spread to square root two times the fundamental precision. It is better to utilize the time taking more measurements of one thing than two things and taking their difference.
Dave
