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    Re: Sextants, vernier and micrometer.
    From: Alexandre Eremenko
    Date: 2006 Oct 31, 08:17 -0500

    
    Henry,
    Close investigation shows that this is a 0.2'
    vernier. Indeed, each degree on the main arc is divided into 6 parts,
    10' each. Now the vernier has 10 big divisions (1' each)
    and each big division is divided into 5 small divisions
    (=1/5 of a minute=0.2').
    This is also confirmed by the certificate which says
    that the vernier reads to 0.2'.
    And accordingly, the table of corrections is given in
    even decimals of a minute.
    
    This sextant seems to have only one visible defect:
    the Index mirror is somewhat deteriorated on its upper edge:
    http://www.math.purdue.edu/~eremenko/pic2.jpg
    and probably needs re-silvering for good performance.
    If you are curious to see the horizon mirror as well,
    it is pic3.jpg.
    
    The seller says that there is no adjusting tool.
    It seems to me that on this type of a sextant, one
    does not need any tool to adjust the mirrors:
    the screws can be rortated with fingers, am I right?
    
    Another question on this sextant: does anybody know
    what were the requirement for a sextant to be qualified
    as Class A? I know the similar requirements for Soviet sextants
    in 1960-s, and they seem to be more restrictive than those British
    of the beginning of XX century.
    
    Alex.
    
    On Mon, 30 Oct 2006, Henry C. Halboth wrote:
    
    >
    >
    > Alex,
    >
    > It looks to me to be a 10 second vernier. Most older sextants/octants had
    > either 10 or 15 second reading verniers.
    >
    > Henry
    >
    > On Mon, 30 Oct 2006 12:42:58 -0500 (EST) Alexandre E Eremenko
    >  writes:
    > >
    > >
    > > Dear George,
    > > Could you look at the picture of the vernier
    > > of that Hezzanith on e-bay we just discussed:
    > > http://www.math.purdue.edu/~eremenko/pic1.jpg
    > > It is supposed to provide 0.2' reading.
    > > What do you think of it?
    > >
    > > One more request. As I understand, you had that
    > > bad sextant (which you returned) in your possession
    > > for few days. Could you recall some detail about
    > > it which would permit to exclude the possibility that
    > > this one is the same?
    > >
    > > Like the number and power of the scopes. Presence/absence
    > > of eyepiece filters?
    > > Anything about the certificate?
    > > Was it a 10" reading vernier? (This one is 0.2' reading).
    > >
    > > Thanks.
    > > Alex.
    > >
    > >
    > >
    > > >
    > >
    >
    >
    > >
    
    
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