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    Re: Precomputing sextant observations at sea
    From: Francis Upchurch
    Date: 2014 Jan 28, 23:15 -0800

    Thanks Gary, yes I think I now understand how and why he did extra LOPs mid flight in addition to pre-flight pre-computed. He needed more pre-computed LOPs for intermediate times like 0400GMT ?, some with new APs and therefore new Hcs via Bygrave?
    The 2 remaining questions from the original chart are therefore:
    1) how did he place his "square box fixes" along the new sun sight LOPs?
    2) how did he calculate that final compass bearing at the turn off point to Howe Is? His pencil markings (bottom left) give bearing 193.3degs resulting from calculation 180+24.3=204.3,-11(?variation 11E?)=193.3degs, presumably magnetic? Where does the 24.3 degs come from?(combination of deviation,drift etc?) I think the -11degs is 11E variation,.I thought the true bearing would have been Az(68degs) +90deg=158deg true.
    Anyways,fascinating stuff.
    For my planned trip, the easiest approach looks to be simple graphs Hp & Az v time as you outlined.Although a short trip, I need 3 rock hopping waypoints where I need to miss the rocks by a mile and turn course, so I recon at least 3 LOPS.I'll show you the plan nearer the time.thanks again.I'll do the odd running fix as well ,just for fun.
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