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    Table on Davis Quadrant
    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

    97

    24

    90

    43

    80

    60

    ½

    99

    10

    96

    29

    88

    47

    77

    63

    ¾

    99

    15

    94

    34

    86

    51

    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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