# NavList:

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

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Re: Classic Trig Log Sight Reduction Revisited
From: UNK
Date: 2014 May 29, 06:51 -0700

This inspired me to finish my "multiple ways to do sight reduction" in Excel. That said, I failed in getting Excel to recognize all the terms and to write everything so each step could be followed. The final result is a mix of Excel, longhand, slide rule, and calculator.

I started this to illustrate how we ended up expressing negative logs as 9.xxx-10 but I ended up not answering that question. Someone smarter than me, and without a calculator, figured that the logCos of 42.175 Deg is -0.13012 and expressed that as 9.869875 -10. It's easy with a calculator but daunting without.

Anyway, the attached is for a different problem, from an Ageton example, with:
Lat 42_10_30
Dec 23_06_24
t 61_33_42 and an answer in Ageton of Hc = 36_01.5 and Az = 90.

In the attached:
First is the input, formula, and answer. Angles as decimal degrees for Slide Rule.
Second is the result with a 10" plastic slide rule similar to a Deitzgen 1733. I was raised with a slide rule and I usually get surprisingly good results if the angles are mid-range.

Third is Cos and Sin as decimals multiplied by calculator with my longhand result in a separate box to the right.

Finally, a calculator used to get logs as negative numbers and making the calculation using those negative numbers. The calculations are repeated to the right in the standard 9.xxx -10 format of the Trig tables.
Regards, Noell
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