# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: 1984 Bowditch question
From: Stan K
Date: 2016 Jul 27, 17:52 -0400
Frank,

You may not like the way Power Squadrons courses are taught, and that's fine, but that's the way it is.  It is not a matter of how accurate the input data is; it is more of a matter of whether the student extracts the correct data from the Nautical Almanac or formula with whatever input data he has.  If two students reduce the same, say, Sun sight, and one has an altitude correction of +12.3' and the other +12.4', only one of them can be right.  Whether the student uses the "approximate" or "exact" dip short formula, it has to be done right or credit is deducted.  Would you want a person who cannot correctly extract data or do simple math to be navigating your boat?

This has generated much more interest than I expected from the question I asked.  Apparently our members like this kind of s**t.

Stan

-----Original Message-----
To: slk1000 <slk1000@aol.com>
Sent: Wed, Jul 27, 2016 4:40 pm
Subject: [NavList] Re: 1984 Bowditch question

This whole thing is a little wacko, isn't it? Worrying about a tenth of a minute of arc for a dip short where the near horizon is 150 feet away is equivalent to believing that you can measure height of eye to a sixteenth of an inch (no way in hell!) or distance to that shore across the little pond to an accuracy of one inch.
Even if that shore is a concrete wall, and you believe it can be defined to the nearest inch, you still have to decide where would that be measured from?? Is it 150 feet from from your retina or your cornea?? Or from the center of the sextant??
Does the navigation student that you mentioned really position his or her feet to an accuracy of one inch?! Good freaking luck! It would be very difficult to repeatably position oneself with a height of eye consistent even to four inches and a distance within five feet. If the observations submitted by this student show apparent accuracies better than about 5 minutes of arc (or internal scatter less than that), then you're probably looking at cooked observations - fraudulent sights. Of course, this probably happens all the time with those USPS programs, myopically focused, as they are, on rote calculation.
Frank Reed
Conanicut Island USA
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