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    Re: Sextant infos
    From: Glendon
    Date: 2002 Jan 30, 1:45 AM

    Hi Pierre and group,
    
    From my watching of Russian sextants, here are my unauthoritative views:
    
    The SNO-T and SNO-M (earlier SNO) are quite different sextants. The SNO-T
    invariably came with 2 scopes ( one Gallilean), most SNO-M with 1, but some
    with 2, and the SNO with 1. The SNO-T seems to be modelled on a late fifties
    early sixties Freiberger, the SNO(-M) on a Plath, probably thirties or
    forties. The frame construction and the screw mechanism are quite different
    between the two. The optics look similar, from photographs I have seen.
    
    I have a 1968 SNO-T in virtually unused condition...the optics are
    excellent, the errors are minimal, its a joy to handle...by which I mean the
    feel is great, although a bit light for some perhaps. I am very interested
    in acquiring a SNO(-M) !!! So, let us know how yours goes.
    
    Lee Martin
    ----- Original Message -----
    From  "Pierre Boucher" 
    To: 
    Sent: Wednesday, January 30, 2002 3:17 PM
    Subject: Re: Sextant infos
    
    
    > >this is a Russian Cetus sextant. I have one.
    > >There should be 2 telescopes. One with cross-hairs which also magnifies -
    I
    > >will have to get mine out to see hat the magnification is... (i'm writing
    > >this from my office). The second eyepiece shows the image the correct way
    > >around.
    >
    > Thanks to Aubrey for the infos.
    >
    > There is only 1 telescope (and support for it) in the box (magnifying with
    > cross-hairs).  No other support for an extra eyepiece.
    > I saw some pictures on the web SNO-T model with 2 eyepieces and SNO-M with
    > only one.  Maybe the other eyepiece could be bought seperately,...
    somewhere!
    >
    > Pierre Boucher
    >
    > **************************************************************************
    >                 X
    >               XX X                                 Pierre Boucher N
    >             XXX XX               formation en navigation de plaisance
    >           XXXX XXX                 Ste-Therese (Quebec) Canada
    >         XXXXX XXX
    >       XXXXXX XXX          la "VOILE"...  le reste n'est que du vent...
    >   XXXXXXXXXXXXXX       ''Sail, Sail !''... the rest is only wind
    >   XXXXXXXXXXXX
    >             XXXX                      EMAIL: pboucher{at}lavoile.com
    >             XXX                               "http://www.lavoile.com"
    > **************************************************************************
    >From-	Navigation Mailing List [NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] on 
    behalf of Glendon [glendonJLM{at}BIGPOND.COM]
    Sent:	Wednesday, January 30, 2002 1:54 AM
    To:	NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject:	Re: Sextant infos
    
    Errk.....make that a 1986 model that I have!! The SNO-M and SNO-T overlapped
    between the late sixties and early seventies, I think.
    
    Lee Martin
    ----- Original Message -----
    From  "Glendon" 
    To: 
    Sent: Wednesday, January 30, 2002 7:45 PM
    Subject: Re: Sextant infos
    
    
    > Hi Pierre and group,
    >
    > From my watching of Russian sextants, here are my unauthoritative views:
    >
    > The SNO-T and SNO-M (earlier SNO) are quite different sextants. The SNO-T
    > invariably came with 2 scopes ( one Gallilean), most SNO-M with 1, but
    some
    > with 2, and the SNO with 1. The SNO-T seems to be modelled on a late
    fifties
    > early sixties Freiberger, the SNO(-M) on a Plath, probably thirties or
    > forties. The frame construction and the screw mechanism are quite
    different
    > between the two. The optics look similar, from photographs I have seen.
    >
    > I have a 1968 SNO-T in virtually unused condition...the optics are
    > excellent, the errors are minimal, its a joy to handle...by which I mean
    the
    > feel is great, although a bit light for some perhaps. I am very interested
    > in acquiring a SNO(-M) !!! So, let us know how yours goes.
    >
    > Lee Martin
    > ----- Original Message -----
    > From- "Pierre Boucher" 
    > To: 
    > Sent: Wednesday, January 30, 2002 3:17 PM
    > Subject: Re: Sextant infos
    >
    >
    > > >this is a Russian Cetus sextant. I have one.
    > > >There should be 2 telescopes. One with cross-hairs which also
    magnifies -
    > I
    > > >will have to get mine out to see hat the magnification is... (i'm
    writing
    > > >this from my office). The second eyepiece shows the image the correct
    way
    > > >around.
    > >
    > > Thanks to Aubrey for the infos.
    > >
    > > There is only 1 telescope (and support for it) in the box (magnifying
    with
    > > cross-hairs).  No other support for an extra eyepiece.
    > > I saw some pictures on the web SNO-T model with 2 eyepieces and SNO-M
    with
    > > only one.  Maybe the other eyepiece could be bought seperately,...
    > somewhere!
    > >
    > > Pierre Boucher
    > >
    > >
    **************************************************************************
    > >                 X
    > >               XX X                                 Pierre Boucher N
    > >             XXX XX               formation en navigation de plaisance
    > >           XXXX XXX                 Ste-Therese (Quebec) Canada
    > >         XXXXX XXX
    > >       XXXXXX XXX          la "VOILE"...  le reste n'est que du vent...
    > >   XXXXXXXXXXXXXX       ''Sail, Sail !''... the rest is only wind
    > >   XXXXXXXXXXXX
    > >             XXXX                      EMAIL: pboucher{at}lavoile.com
    > >             XXX                               "http://www.lavoile.com"
    > >
    **************************************************************************
    > >From-	Navigation Mailing List [NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] on 
    behalf of Chuck Griffiths [griffiths_chuck{at}SI.COM]
    Sent:	Wednesday, January 30, 2002 7:30 AM
    To:	NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject:	Re: Fluxgate compass
    
    OK, I'll throw in my fluxgate question that has been eating at me since I
    installed a fluxgate for my autopilot a couple years ago.
    
    When one first installs a fluxgate, I would imagine that it has two errors.
    First, when the ship is on a heading of exactly "0", relative to local
    variation, the fluxgate reads something other than north, due to deviation (the
    disturbance of the sensor by magnetic fields on the ship). Second, all other
    headings will also have deviation induced errors, e.g. the display indicates 80
    degrees when it should read east.
    
    Now, I can imagine that after the compensating program is run, the fluxgate
    could compare the rate of turn indicated during the compensating turns and
    adjust indicated headings such that they match headings as they should have
    appeared during the turns. To continue my example, the fluxgate could sense the
    rate of turn and know that 90 degrees of turn have been completed so the display
    should indicate east, the previous error between 80 and 90 degrees could be
    corrected. But, how does making constant rate turns help the fluxgate find
    magnetic north if it sensed it incorrectly to begin with? Of course, I checked
    it after I corrected it by comparing headings to sun bearings so I know it
    works, I'm just wondering if someone can explain how it works.
    
    
    ____________________Reply Separator____________________
    Subject:    Re: Fluxgate compass
    Author: Brian Whatcott 
    Date:       1/29/02 6:33 PM
    
    At 05:16 PM 1/29/02, you wrote:
    >... What exactly
    >is a bolt-down sensor? And what errors does it "abolish"?
    >
    >As I understand it, a fluxgate compass, like any other compass, needs to
    >establish the direction of the horizontal component of the Earth's field,
    >with respect to the direction of the vessel. For this to happen, somehow
    >the fluxgate compass, just like any other compass, has to be aware of the
    >direction of the horizontal. ...
    >George Huxtable.
    
    
    George, the comments I posted were on the basis of examining the
    constructional details of a fluxgate.   In view of your praiseworthy
    efforts in describing the Lunar, I'll try to return the favor by taking
      a look at what the commercial fluxgate offerings provide.
    
    It may be that for a 2-axis fluxgate, a pendulous mount might be adopted.
    This would retain the pendulous errors associated with a compass card
      of the conventional kind. I'll get back to the list, if I find useful
    engineering input.
    
    A three axis fluxgate can be mounted rigidly. This is sometimes called a
    'bolt-down' sensor.
    
    
    
    
    
    
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