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    Re: Bubble Sextant
    From: Bill Morris
    Date: 2008 Jul 10, 22:40 -0700

    The British Mk IX is about 200 grams lighter. and is  my favourite
    because all the controls come readily to hand, it is easy to use and
    read and you have a reasonable chance of getting one that works. With
    the exception of the averager on the Mk IX A, the works of the Mk IX
    series are accesible and usually easy to fix. The bubble assembly is
    also easy to refill.
    My A7 has a vapour pressure bubble chamber which, if empty when you
    get it is very difficult for the non-specialist to refill. Many of the
    WW II US instruments suffered from "complification" and some used 4
    prisms, heavy and expensive to produce. The AN 5854-1's
    averager(strictly, a median device)is temperamental and hard to fix if
    it has suffered corrosion in storage. The AN 5851(Navy Mk 5)is heavy
    and clunky and initial setting of its averager needs care. The A10-A
    is perhaps the handiest instrument to use, provided the electrical
    marking system is in good order. It is not impossible for
    a reasonably handy person to fix the system, once it has been
    understood. The A10 uses the Mark I finger to operate the marking
    pencil. That leaves rarer instruments, like the A8-A and the Navy Mk
    IV. The latter was plainly not a success and if you find one, the
    averaging system will tax the average person to fix. The A12 is a
    favourite of many people and was designed to be cheap to produce(some
    of the others cost almost the price of a small home to produce). The
    arc and vernier on mine are poorly cut, but if you can get one free
    from corrosion and in working order it would be a good one to start
    The Achilles heel of nearly all the bubble sextants is the bubble
    chamber. For practical purposes, you cannot refill a vapour pressure
    chamber. Happily, most of the later bubble sextant produced used a
    different system with an air reservoir; and these are fairly easy to
    refill. The MA series are, alas, expensive and do not often come on to
    the market.
    Bill Morris
    On Jul 11, 1:54�pm, "Gary J. LaPook"  wrote:
    > My fravorite is my MA-1 which isn't a bubble sextant but a pendulous
    > mirror type and my second favorite is the MA-2 with a bubble. If you
    > want a light, simple sextant get a Bendix A-7, it is the lightest bubble
    > sextant I have.
    > gl
    > glap...@pacbell.net wrote:
    > >Here is a link to a site with discriptions of many types of bubble
    > >sextants:
    > >http://home.earthlink.net/%7Es543t-24dst/airnav/index.html
    > >gl
    > >On Jul 5, 3:19 am, glap...@pacbell.net wrote:
    > >>You should also check the files section of the Yahoo sextant group for
    > >>more information on sextants.
    > >>http://groups.yahoo.com/group/Sextants/files/
    > >>gl
    > >>On Jul 3, 5:14 pm, bubi352  wrote:
    > >>>I am new to this group and new to celestial navigation. I currently
    > >>>work as an airline pilot and fly extensively over water at night. I
    > >>>have developed a keen interest in determining my position the old
    > >>>fashion way.
    > >>>Could someone tell me which bubble sextant I should buy?
    > >>>What should I be looking on a bubble sextant?
    > >>>Where can I buy one?
    > >>>Thank you in advance.
    > >>>Bubi- Hide quoted text -
    > - Show quoted text -
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