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    Re: Appeal to forum members to collect data
    From: Henry Halboth
    Date: 2007 Oct 25, 11:45 -0700

    Hi Al,
    The proposal sounds intersting to me with but one
    exception, i.e., the use of Frank's on-line calculator
    as a standard to determine error. This may be a
    perfectly sound approach, yet I simply don't know the
    basis for or the accuracy to which this calculator
    works - at very least it is rounded off to tenths
    which in itself leads to possible comparitive errors.
    In my view, a purpose of the Lunar Observation was to
    determine Longitude based on time difference. Simply
    stated, my interest is in Position finding, not
    measurement accuracy, and this requires a full round
    of observations to arrive at. It appears that a truer
    gauge of error would rest in a comparison of Lunar
    determined Longitude with the known position of
    observation. There really should be no problem with
    the actual distance measurement itself, given a decent
    instrument and a reasonably competent observer.
    I am not insensitive to the fact that this approach
    requires more work, both calculative and in the
    observation of the necessary altitudes, whether by sea
    or artificial horizon, but then this was all a part of
    the original Lunar solution.
    --- Jim  wrote:
    > I would like to collect some data from a variety of
    > observers using a
    > variety of marine sextants taken in a uniform
    > manner.
    > What I am proposing is to collect data using the
    > following method:
    > 1. Take 5 observations (moon and sun, star or
    > planet) standing on
    > land. No graphing, just 5 raw observations.
    > 2. Record name of observer, sextant used, power of
    > sextant scope, GMT,
    > date, Lat and Long, name of body used, distance
    > (corrected with IE),
    > barometric pressure, temperature, error in each
    > observation (in
    > minutes)
    > 3. I would propose using Frank's online calculator
    > to evaluate the
    > error in each observation using the known lat and
    > long and letting it
    > calculate the heights of the moon and body observed.
    > 4. Angular measurements reported in whole degrees
    > and minutes rounded
    > to the nearest 0.1'.
    > 5. Make the observations in good conditions and with
    > the moon and body
    > 15 degrees or more above the horizon.
    > 6. Submit the results to me and I will accumulate
    > the data in tabular
    > form. I could provide an Excel template to use or
    > the results could be
    > sent in a set text format.
    > My ambition in doing this would be to have some
    > clear cut answers to
    > the accuracy and precision questions that come up.
    > What I have found
    > is that although there have been many postings on
    > the topic, there is
    > always some question as to how the observation(s)
    > were taken, the
    > method of evaluation used or what almanac data was
    > used.
    > Once in electronic format we could proceed to
    > analyze the data in a
    > multitude of ways.
    > I would invite comments on this proposal at this
    > point and will remain
    > hopeful that a few people out there would like to
    > join the endeavour.
    > Jim
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