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    Re: Using star-star distances
    From: Hewitt Schlereth
    Date: 2008 Sep 24, 00:42 -0400

    Thanks for the fast response.  I'll look around the net for Plastimo.
    Earlier I did find an outfit in France that sells Ebbco, but their
    list of spares did not include what I wanted.
    Further FWIWs: 1) My practice with the Ebbco was to check IE at the
    beginning and end of a round of sights and average. As a rule the
    result was around 1' IE. 2) One day I took morning and afternoon sun
    sights from the top of the Gibbs Hill Light in Bermuda with my Ebbco,
    my C. Plath and my vernier Davis. The resulting fixes were: 1 mile for
    the Plath, 2 miles for the Ebbco, 4 miles for the Davis. 3) On the two
    occasions I was able to compare my Plath results with a Satnav, one
    came out spot-on with the longitude and 2' different on the latitude.
    The next time (different boat) I was spot-on with the latitude and 2'
    different vis-a-vis the longitude.
    On 9/23/08, frankreed@historicalatlas.net  wrote:
    >  Hewitt S., you wrote:
    >  "I'm trying to restore an Ebbco sextant. What I need is a set of shades and
    >  the spring retainer for the horizon mirror or an entire horizon mirror
    >  assembly. The model I have is the later one with the larger mirrors and
    >  three index-mirror shades."
    > If you don't get any hits on this after a week, let me know. There are
    >  several at Mystic Seaport (for classroom use, not in the collections) that
    >  are in various states of repair, and it may be possible to cannibalize the
    >  parts you need.
    >  And you wrote:
    >  "FWIW : I used an Ebbco for years and it always stayed true to the DR
    >  and always got me there."
    > True to the DR meaning...? As long as the fix and the DR were not more than
    >  perhaps five miles apart, you would have considered that acceptable, right?
    >  So random errors even as large as +/-2 minutes (on top of inescapable
    >  observation errors) would have been hard to detect in the pre-GPS era.
    >  Just so there's no misunderstanding, I always recommend plastic sextants to
    >  people who want to do standard, basic LOP celestial navigation. But I would
    >  note that I frequently find that the sorts of people who are interested in
    >  celestial today are also interested in owning an instrument that they can be
    >  proud of, and for reasons which are only partly rational, plastic sextants
    >  don't make the cut.
    >   -FER
    >  >
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