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    Re: Error of Perpendicularity
    From: Alexandre Eremenko
    Date: 2006 Apr 18, 08:17 -0400

    The symbol ^ represents power. So L^2
    means L squared (multiplied by itself).
    Here is the same formula in words:
    Error in seconds equals
    negative 2 times sin1" times (error in perpendiculatiry, squared) times
    tangent of one quarter of the angle.
    Hope this helps.
    I bought Chauvenet in some web book store for much less
    than $300. I don't think I payed more than $50 for the
    set of two volumes in excellent condition.
    (I don't remember what the exact price was, but I would
    definitely not buy it for more than $50, because my
    university library has it, and the library is next to
    my office. So yesterday I used the library copy to reply
    your message quickly:-)
    On Mon, 17 Apr 2006, Robert Eno wrote:
    > Thanks Alexander
    > Quick question:
    > Does the ^ symbol represent multiplication?
    > I am having a bit of trouble following the sequence of calculations in the
    > formula.
    > 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
    > me.
    > cheers,
    > Robert
    > ----- Original Message -----
    > From: "Alexandre E Eremenko" 
    > To: 
    > 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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