# NavList:

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

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Re: Fw: Sight Reduction by Hand you might like
From: Hanno Ix
Date: 2014 Jan 1, 20:29 -0800

Alex:

I just saw this posting of yours.

There is EXCELLENT reasons for NOT using logarithms when doing sight reduction by hand.

Or rather, there is EXCELLENT reasons for using the method as described in the posting g24866/.

1. The method asks for working only with 4-digit integers. The operations are
limited to: addition, subtraction, division by 2 and division by 4.
NO multiplication.

2. It requires just 2 (two!) pages of a table - much less than MT-43.

2. It does so with an error of +-0.5 min from 0 to 90 deg. - i.e. above
85 deg!

3. The method will work for all combinations of declination, latitude
and hour angles - no need to consider any special cases.

4. It is easy do teach and to memorize.

By comparison, the literature on CelNav with logarithms, even by acclaimed experts, contains many examples that are seriously wrong. No wonder: log methods require 6 digit calculations, cannot deal with negative angles and cannot deal with angles close to 0 and 90 degrees. Therefore one can get easily lost in the consideration of special rules that apply in those cases.

The real "problem" of any sight reduction by hand is the "by hand" part, of course. I know because I am certainly not good at it myself. But that is where its nobility lies: the simplicity and the challenge for mental acuity and discipline.

I wish you could spend some time to go through an example or two. I'd love to hear what you thought when you were done.

Hanno

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