# NavList:

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

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Re: Cryptic Slide Rule Formulae
From: Gary LaPook
Date: 2016 Jan 20, 21:32 +0000
Formula 1 is the standard sine-cosine formula for Hc.
Formula 2 is the standard formula for azimuth.
Somebody else can figure out the other ones.

gl

To: garylapook@pacbell.net
Sent: Wednesday, January 20, 2016 1:22 PM
Subject: [NavList] Cryptic Slide Rule Formulae

Hello,
My father-in-law, who sailed for years out of Huntington, LI, passed away a year ago.  In one of his desk drawers I found a 10" Sterlin Slide Rule, No. 584.  It is white plastic, not very eleborate.  (however, still beyond my slide rule skills!)  He had scratched the following 7 formulae on it.  I am just wondering if anyone would recognize the text or method he was using this rule for:
In no particular order:
1.     sin h = sin L sin d + cos L x cos d cos t
2.     sin z = cos d sin t sec h
3.     cos co-d = cos co-h cos co-L + sin co-h sin co-L cos z
4.    sin t = (sin z sin co-h)/sin co-d
5.    cos t = tan d cot L
6.    sin h = sin d csc L
7     sin A = sin d sec L
Thanks in advance for any insight into this....
Darden Rives

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