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    DR formula
    From: Doug Royer
    Date: 2003 Oct 17, 09:58 -0700

    Axel,here is an explaination of the formula.I use it on a programmable Casio
    calculator and get the Lat. and Lon. of the calculated DR very quickly.It's
    always very close to the pos obtained by dividers and rules on a paper chart
    or DR software.I believe I wrote the formula for Long. wrong.It should be
    written as delta Long.
    Lat. = latitude of DR
    Lf = Latitude of last fix.
    + - e = time in hrs since last fix. + e for calculating Lat after last fix.
    - e for calculating Lat before last fix.
    S/60 = speed in kts./ 60
    cos T* = cos of the true course in * ' "
    Long. = longitude of DR
    Lonf = longitude of last fix
    + - e = same as above
    S/60 = same as above
    sin T* = sin of true course in * ' "
    cos Lf = cos of latitude of last fix in * ' "
    A note about the Longitude of the DR: when useing this formula you will,if
    travelling in a westerly direction,add the above Long. answer to the Lonf to
    get the DR long. If travelling in an easterly direction subtract the answer
    from Lonf to get the DR long.

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