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

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Re: Fw: Chichester's Calculations ( Sine-Cosine method)
From: Gary LaPook
Date: 2008 Dec 12, 03:44 -0800

```I also decided to work Chichester's example using my Bygrave Slide Rule
since Chichester used one of these when he flew his Gypsy Moth airplane
from New Zealand to Australia in 1931. I came up with an Hc of 46º 26',
Az of 57º10' the same as Chichester got. I have attached this computation.

gl

Gary J. LaPook wrote:
>
> I decided to work the same example using the standard Sine- Cosine
> method to compare it to the Haversine-Cosine method. I discovered that
> it takes fewer table entries and additions than does the Haversine
> method so I do not know why that method became the prefered method, any
> ideas?
>
> I am posting and example of this computation. I am also attaching a PDF
> of it to ensure that the format doesn't become corrupted.
>
> ﻿The normal formulas for computing Hc and azimuth are:
>
> sin Hc = sin Lat  sin Dec + cos Lat cos Dec cos LHA
>
> and
>
> sin Z = (sin LHA cos Dec)/ cos Hc
>
> rearranged to the more convenient
> sin Z = sin LHA cos Dec sec Hc
>
> These can be solved using logarithms  using this format:
>
>
>

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