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    Re: Question about Pub 249 combined Star and Planet sight reduction
    From: Rod Deyo
    Date: 2000 Nov 20, 8:36 PM

    My thanks to Richard B. Emerson, Dan Allen, and Paul Hirose for their
    responses. A few further comments:
    1) Perhaps the issue is moot for small craft when the measured Hs values are
    uncertain, but as you get away from the epoch used for Pub 249 Vol 1
    calculations, the nutation and procession corrections are as large as 4 nm .
    I hate to just give away that amount of error on what otherwise might be
    consistent sights.
    2) The question I raised was how to properly weight multiple LOPs when some
    of them are intended to be corrected as a single group. Just eyeballing the
    answer is tough for me if there are five LOPs, three which need to be moved
    a few miles in a particular direction (for example, several Pub. 249 Vol 1
    star sights corrected for nutation and procession) and then weighted against
    two that are not shifted (several planet or other star sights not done using
    Pub 249 Vol 1, but using the Almanac and 249 Vols 2-3 or Pub 229). Ideally,
    you then pick the point as your final fix that minimizes the square of the
    distance from each of the corrected LOPs (this is an unbiased estimate,
    since no line or set of  lines is favored over the others).
    3) At the moment, I've convinced myself that it's probably best to either a)
    assume it makes no real difference and do not correct (this is probably good
    enough if the correction is 1 nm or less) or b) correct each AP by the
    nutation and procession, plot the resulting LOPs, and then eyeball each of
    the LOPs together to get the final fix.
    Rod Deyo

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