NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Testing Scopes
From: Bill B
Date: 2006 Apr 20, 00:06 -0500
From: Bill B
Date: 2006 Apr 20, 00:06 -0500
Alex Thank you for a thorough look at the scopes. > Remarks. Observations with |4SD-true.4SD|>.4 are discarded > as SNO-T manual recommends. As you know, I have some problems with 4SD comparisons where SD is taken literally from the almanac. Discarding observations where |4SD-true.4SD|>.4 has to take into account mental interpolation of the almanac SD to be workable IMHO. For example: Date SD 4SD March 28 2006 16.1 64.4 March 29 2006 16.0 64.0 April 21 2006 16.0 64.0 April 22 2006 15.9 63.6 A change of nominally 0.005' in reality can cause a change of 0.1' SD in the almanac. If identically observations are taken a day apart near a rounding up or down, one might pass the test and the other not. If we interpolate around March 28/29 we have a more realistic 4SD of 64.2 to compare our observations against. In the worst-case scenario using the|4SD-true.4SD|>.4 rule around March 28/29, +/- 0.2' error is already introduced into 4SD if using the almanac figures directly. That leaves 0.2' operator and sextant error for two tangency observations, or < 0.1' error per tangency. That's a tough mark to hit, and otherwise usable observations might be discarded (false negative). On the flip side of the coin--if it works the other way, some very sloppy observations might pass the test resulting in a false positive. Bill
