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    Re: R: Re: R: Solutions to Gray's 100 Problems (Problem 1-1)
    From: George Huxtable
    Date: 2007 Sep 27, 19:53 +0100

    Parsa wrote-
    | I need advice on the sextant height corrections.
    | I also did all the calculations on my Palm TX using CelestNav
    | software.
    | It gives the option of rounding or not rounding the assumed position.
    | When I set it to round, I'm happy to see that it gives an identical Hc
    | to mine. The GHA was a bit different between the Palm and the table
    | (336 23.6' on the Palm, 336 23.4' from the nautical almanac with v
    | correction.). LHA still works out the same though and the final Hc on
    | the Palm is +14 52.9', while I had +14 53'.
    | The difference is in observed height (Ho). Applying all the
    | calculations, I had:
    | Hs=15 15.3'
    | -2.5' for 7 feet Dip (I did it using a formula too and it came to
    | -2.6')
    | -1.2' index correction
    | Ha=15 11.6'
    | -3.5' for app. altitude
    | +0.3' additional correction for Venus on May 13, 1993
    | Final Ho=15 08.4'
    | However, my Palm program gave Ho as Ho=15 10.3' resulting in a LOP 2nm
    | different than mine.
    | That 2 minutes off gave a difference of 2nm. Am I splitting hairs, or
    | did I do something wrong?
    | I want to understand the sextant corrections before I move on since I
    | have to do them for every problem.
    Comment from George-
    Yes, quite right, you need to track such discrepancies down. A difference of
    0.1 or 0.2 might well result from different roundings-off, but a 2-minute
    difference shows something is wrong. You are not splitting hairs.
    I'm not familiar with the details of the problem that Parsa is tackling, nor
    with the CelestNav software. But that part of the calculation is only a
    matter of simple arithmetic.
    It may just be a matter of definition. Index error is a likely source of
    confusion. Sometimes, it will be asked-for in terms of index correction;
    otherwise as index error, with the opposite sign. Are you sure that you, and
    Celestnav, are treating it the same way? Try putting in a silly value, such
    as 100', for index error, and see if the two results diverge further, or
    whether their difference stays the same. That's often a useful trick to
    apply, when things go wrong.
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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