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    Re: Using star-star distances
    From: Bill Morris
    Date: 2008 Sep 24, 02:51 -0700

    On the only EBBCO I owned, the shade glasses were a sandwich of some
    sort of coloured material, possibly a coloured resin, between two thin
    sheets of glass. The sandwich was held in the shade mount by a thin
    plastic annulus that snapped into and could be snapped out of place.
    Mine was very old when I bought it and the coloured material had
    degraded to a sticky, totally opaque mess in all but one of the
    shades. I separated all the sandwiches, after a soak in a solvent
    whose nature I cannot now remember, breaking one or two of the sheets
    of glass in the process. To renew the shades I used two sheets of self
    adhesive polarising film glued one on top of the other to a single
    sheet of glass at a suitable rotation to give various shades of grey.
    The film was quite tough to cut, but any rough edges were concealed
    beneath the retaining rings. The shades worked well without noticeable
    distortion. I didn't test for prismacity and doubt that it could have
    been detected against the background of continuous and unpredictable
    change in index error. I hated the whole instrument and sold it as
    soon as possible thereafter.
    Plastimo is indeed now the agent for the instrument.
    Bill Morris
    On Sep 24, 2:05�pm, "Hewitt Schlereth"  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.
    > Ebbco doesn't have a web site and the letter I wrote them came back
    > with a laconic note "moved." (Be nice if it had said where).
    > FWIW : I used an Ebbco for years and it always stayed true to the DR
    > and always got me there.
    > Hewitt
    > On 9/23/08, Bill  wrote:
    > > �George wrote
    > > �> That's interesting, and rather a surprise to find such extreme
    > > �> bad-behaviour. Was the index error similarly unstable, or did the index
    > > �> error stay put while the calibration changed? What were the conditions of
    > > �> the test? Had the instrument been given any time to stabilise, in
    > > �> temperature? Presumably, the instrument had been checked-over to ensure that
    > > �> no mirrors or brackets were at all wobbly
    > > If you have not checked out David Burch's field tests of plastic sextants,
    > > �Frank's figures might seem a bit high, but they are pretty much in line with
    > > �Burch's findings.
    > > �Bill B.- Hide quoted text -
    > - Show quoted text -
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