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    Re: Error of Perpendicularity
    From: Robert Eno
    Date: 2006 Apr 17, 20:56 -0400

    Thanks Alexander
    Quick question:
    Does the ^ symbol represent multiplication?
    I am having a bit of trouble following the sequence of calculations in the
    Any chance of your scanning in that particular page and sending to me?
    I've always wanted a copy of Chauvenet but the $300 plus price tag deters
    ----- Original Message -----
    From: "Alexandre E Eremenko" 
    Sent: Monday, April 17, 2006 2:21 PM
    Subject: Re: Error of Perpendicularity
    > Dear Robert,
    > The only book I know that contains a COMPLETE
    > theory of sextant is Chauvenet. (I am sure that there
    > are others, but this is really complete, very concise,
    > and written in good English:-)
    > In particular, on p. 115 (vol. 2) the following formula
    > is derived:
    > Err=-2 L^2 sin1" tan(h/4),
    > where Err is the resulting error, in seconds
    > L is the deviation of your mirror from
    > perpendicularity (in seconds) and h the angle you measure.
    > In more modern notation this becomes:
    > Err=-0.00057 L^2 tan(h/4)
    > where both Err and L are in minutes now.
    > For example, if L=5'
    > Then Err=0.008 or 05", which is completely negligible.
    > Now, according to SNO manual, you can adjust this mirror
    > (using special factory-supplied visors in place of dominoes)
    > That's why visual adjustment (without dominoes) is OK too.
    > Two years ago there was a large discussion on the list about
    > how exactly to do this adjustment, and the general conclusion
    > was that dominoes (or visors) are only recommended for sextants
    > with front-silvered index mirros.
    > For back silvered mirrors, the usual eye method is OK.
    > Alex

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