# NavList:

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

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Re: Were Short methods really Short?
From: Greg Rudzinski
Date: 2016 Aug 5, 20:20 -0700

David,

Amplitude:

Dec A - Lat B = Inv A = Z  (apply +/- to 90° or 270°)

You are probably looking at a first generation form with errors.

Greg Rudzinski

From: David C
Date: 2016 Aug 5, 19:12 -0700

The work sheet for Ageton Classic has entries for Prime Vertical calculations. The second of the calculations uses the formula for amplitude at rising
sin A = sin d * sec L.

The worksheet (incorrectly I believe) describes the result as Z.

On 17 July 2016 when L = S41° 06.5'  and  d = N21° 08.6'   Ageton Classic gives  Z=28° 36'.  An app gives the sun's azimuth at rising as 62.3° or 62° 18'.

28°  36' +  62° 18'    = approx 90°.  Why the result is not exactly 90° is probably a thread in itself (unless I have made an error in my calclations).

As a check, for Lat  41° and Dec 21° Table 27 in Bowditch gives amplitude = 28.3° or 28° 18'.

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