# NavList:

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

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From: Nicolàs de Hilster
Date: 2007 Sep 22, 09:47 +0200
Dear group,

last week I got in contact with an owner of a Davis Quadrant. On the back of the large arc the following table is inscribed:

 L D L D L D L D ¼ 100 5 1¼ 97 24 2¼ 90 43 3¼ 80 60 ½ 99 10 1½ 96 29 2½ 88 47 3½ 77 63 ¾ 99 15 1¾ 94 34 2¾ 86 51 3¾ 74 67 1 98 20 2 92 38 3 83 56 4 71 71

In simplified form we could change this into:

 L D 0.25 100 5 0.50 99 10 0.75 99 15 1.00 98 20 1.25 97 24 1.50 96 29 1.75 94 34 2.00 92 38 2.25 90 43 2.50 88 47 2.75 86 51 3.00 83 56 3.25 80 60 3.50 77 63 3.75 74 67 4.00 71 71

The table lacks an entry for 0.00, which would most probably have read L=100 and D=0. The figures in columns L and D can also be calculated using simple math:

L=COS(a*b)*100
D=SIN(a*b)*100

In above formulae 'a' stands for the value in the first column (so 0.25, 0.50, 0.75 etc) and 'b' is a constant. Using the least squares method I was able to calculate 'b' as 11.266, so the formulae used were:

L=COS(a*11.266)*100
D=SIN(a*11.266)*100

Question that remains is: what use was this table to a navigator?
Anyone any idea?

best regards,
Nicolàs

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