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    Re: Sextants, vernier and micrometer.
    From: Henry Halboth
    Date: 2006 Oct 31, 19:57 -0500

    Alex & George,
    
    I must apologize for not having viewed the vernier picture properly. You
    are quite correct in stating it to be a 12-second vernier, which does
    prove that I have most certainly not seen everything or read everything
    either for that matter. It is, however, rather amazing that I have not
    run into this before - I presently own 3-vernier sextants, and any number
    of a vintage equal to yours have passed through my hands over the years,
    and I simply have never seen other than 10 or 15-secnnd verniers.
    
    Again, my apologies.
    
    Henry
    
    On Tue, 31 Oct 2006 08:17:49 -0500 (EST) Alexandre E Eremenko
     writes:
    >
    >
    > 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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