# NavList:

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

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Re: Ogura IJN
From: Stan K
Date: 2017 Aug 9, 20:14 -0400
Greg,

You said,
The arc sin of  (sin declination divided by sin latitude) = PV.
Isn't that formula for the altitude of a body on the prime vertical, and doesn't it only apply if latitude and declination have the same name and dec<lat?

Stan

-----Original Message-----
To: slk1000 <slk1000@aol.com>
Sent: Wed, Aug 9, 2017 3:45 pm
Subject: [NavList] Re: Ogura IJN

David,
You might want to give a slide rule a try for solving azimuth. I like slide rules that have the S scale just above the C scale on the slide (see Post Versalog 1460). First solve for prime vertical if the quadrant of the meridian angle is in doubt. The arc sin of  (sin declination divided by sin latitude) = PV.  To solve for Z = arc sin (cos dec sin t / cos Hc) . Use Zn rules to get azimuth. I prefer the slide rule to the Rust diagram seen in Weem's Line of Position Book. The Ix graph is the best compact azimuth method and fits on one side of a standard sheet of paper. All useful formulae and rules can be jotted down on the blank back side for inclusion into a short table, sextant box, or wallet.
Greg Rudzinski

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