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    Re: Death to the Intercept Method!
    From: Francis Upchurch
    Date: 2016 Nov 5, 03:35 -0700

    Thanks Frank,

    I agree with  you re the modern time sight. I still use the intercept LOP method, mostly because I enjoy using the Bygrave and Browne Nassau which are set up for that. If I am going to use calculators, however, I've discovered that a "relatively cheap" Casio fx-3650P can take up to 4 cel nav programes, then this works best for me. Far less mistakes from pressing the wrong buttons. Just 3- 6 basic inputs.

    One of my favourites is the 2 body simulataneous time sight which gives lat and long direct.

    Simultaneous Time sights for Long and Lat. Formulae from Karl page 78-79 (131 bytes)

    Inputs: d1(>A) and d2(>B). Dec of the 2 bodies.

    GHA1 (>C)and GHA2 (>D) GHA of the 2 bodies

    H1 (>X) and H2 (>Y) Alts of the 2 bodies.

    Find D12 = great circle GP1-GP2


    1)Cos D12=sind1sind2+cosd1cosd2cos(GHA1-GHA2)



    1)      Cos B=(sinH2-cosD12sinH1)/sinD12cosH1

    (sinY-cosMsinX)/sinMcosX: Cos-1Ans>Y:

    2)      Cos A=(sind2-sind1cosD12)/cosd1sinD12

    (sinB-sinAcosM)/CosAsinM:cos-1 Ans-Y:Ans>Y:


    3)      Sin Lat=sind1sinH1+cosd1cosH1cos(A-B) (Cos (A-B) now in Y)

    sinAsinX+CosACosXCosY: sin-1Ans>Y:


    4)      Cos LHA1=(H1-sind1sinLat)/cosd1cosLat



    5)      Lon=LHA1-GHA1


    Dec 1=75˚>A. Dec2=30˚>B.GHA1=30˚>C, GHA2=320˚>D, H1=60˚>X, H2=45˚>Y.

    Gives answer Lat 68˚31’N , long 80˚17’ (East+ and west-)


    Dec1=7˚24.4’N, Dec2=-11˚7.7’S,GHA1=37˚52.9’, GHA2=285˚23’,H1=30.3861˚, H2=20.77519˚. Gives Ans Lat35˚, long 20˚.

    My ideal is a "no clock" "simultaneous" moon- sun fix and lunar for GMT. 

    Recently, I've  used the Bygrave for the 2 LOPs and the Fuller 3 for the lunar GMT, using your version of the Thompson abbreviated clearance method.(Also the occassional Margett graph clearance, just for fun). Both are now pre-programed on my Calculator and give virtually instant accuracy check on my slide rule and Margetts calculations. Great fun.

    Best wishes


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