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On Oct 25, 2:45 pm, hch  wrote:
> 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.

The intent here is that the method of calculation and the almanac
source is consistent for whole data set. Certainly someone could take
the data later and rework it using different methods. I'm sure if
Frank reads this he would be more than willing to offer some comment
as to the level of accuracy of his program.

Perhaps even more important is that clearing the data online is very
convienient and will hopefully facilitate participation.

>
> 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.

This is essentially what we would be doing. By entering the known lat
and long in Frank's online calculator we find out how far out our
lunar distance is be it expressed as time or angular difference.
>
> 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.

Just to clarify I am asking for sets of 5 meansurements and would take
as many sets as anyone is willing to send me.
>
> Regards,
>
> Henry
>
>
>
>
>
> --- 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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