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    Re: C. Plath Sextants Mirror Adjustment
    From: Kieran Kelly
    Date: 2003 Sep 16, 18:42 +1000

    I recently posted the following request on the sextant list but have had no
    reply:
    
    I am seeking information on the mirror adjustment mechanism on the Plath
    Navistar Professional which is substantially different from that on the
    Plath Classic.
    
    One reply received said:
    >First of all, it's not a matter of loosening (and re-fastening) screws,
    we're only talking
    >about adjusting screws. These are the ones with the square head for which a
    special key is
    >provided with the sextant (at least, it should be).
    
    My reply to this was:
    This is certainly the case with the Plath Classic as it has two square
    headed adjusting screws on the horizon mirror and a single square headed
    adjusting screw on the index mirror and is simple to adjust with the special
    tool provided.
    
    The horizon mirror of the Plath Navistar Professional however has two
    hexagon shaped adjusting screws for which the special tool is used plus a
    third screw, headed for a screwdriver. All these screws are on the back of
    the mirror housing. The index mirror on this sextant has one adjusting screw
    plus a conventional screw all on the back of the housing. The extra screws
    appear to be designed to hold the mirrors in the frame. What do you do with
    these screws? Do they have to be loosened while the adjustment process is
    made then tightened when all is in alignment? This is the process with some
    of the English sextants. I am frightened if I try the adjustment with this
    screw done up tight I may break the mirrors.
    
    I have checked the exploded view of the Plath Professional sextant which
    comes with the manual and it shows the conventional screws holding the
    mirror retaining springs in place however it is silent on what should be
    done with these screws when adjustment is made.
    
    Note that Bauer's The Sextant Handbook cautions on page 55 that the
    navigator must always loosen one screw when adjusting the mirrors on a
    sextant before tightening the other otherwise the glass will break. Does
    anyone know if this applies to the two adjustment screws on the horizon
    mirrors of the Plath Classic and Professional sextants? Any help would be
    appreciated.
    
    Regards
    
    Kieran Kelly
    
    
    

       
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