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    Re: sextant
    From: Peter Fogg
    Date: 2008 Feb 19, 12:44 +1100
    Dan
     
    What do you and Sara want to do with this sextant?  The answer to this question may have a lot to do with how relevant the responses to your questions may be.
     
    Sextants are precision instruments; a lot of care goes into making them read angles as accurately as possible.  Most (maybe all) of the well-known brands do this very well, to the extent that the accuracy of the instrument is usually not the limiting factor in achieving the best possible results from them.  Other factors come into play, such as recording the time accurately, and achieving the best result possible from a number of sights, each of which may have random errors.  And other factors which have little to do with the instrument itself.
     
    In any case, a sextant is a hand-held instument; a limitation in itself.  They were designed to be used in situations where a stand-mounted instrument could not be set up, such as from a boat. Surveyors use theodolites, which are tripod mounted instruments, one reason they are capable of greater accuracy than sextants (in practice surveyors also pay attention to those 'other factors' in order to achieve best possible results - they really are important when it comes to accuracy).
     
    Finally, are you sure you mean accuracy and are not confusing this with precision?  If an instrument is capable of reading an angle to the nearest second of arc then that is great but it is only an indication of its level of precision.  It doesn't, by itself, tell you anything about how accurate that reading may be ...

    On Feb 19, 2008 12:23 PM, Sara and Dan <slhdem@valstar.net> wrote:

    Which brand of sextant and from what era is the most accurate?

    Tamaya has a very good reputation and many are certified without any arc
    error, but this sextant has no verneer on the
    micrometer so can you read it to more than about 15 seconds of arc?

    I think the same is true of c.plath

    The U.S. wwII sextants have a verneer and so can be read to what about 5
    seconds? but the listed corrections
    are in the 25 to 30 range

    The russian sextants have a magnifying glass to look at the micrometer
    but no verneer

    What other issues should one consider in choosing the type most likely
    to be as accurate as possable?

    I am interested in hearing any opinions out there.

    Also I never did get anyone who commented on my question about the deck
    watch with the ten hour dial. Was this
    used for some type of navigation or what purpose  ( the watch has a
    secondary  more conventional twelve hour dial also)

    Dan

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