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    Re: Perpendicularity again. was: Adjusting Central Mirror
    From: Gary Harkins
    Date: 2004 Oct 11, 21:13 EDT
    In a message dated 10/11/2004 7:04:52 PM Eastern Standard Time, eremenko{at}MATH.PURDUE.EDU writes:
    The simplest one and most common one says:
    look into your index mirror so that you see a part of the arc
    and another part of the same arc reflected in the mirror.
    If everything is OK, you see the arc as a straight continuation
    of its reflected image.
    As I understand it this only works if the mirror is silvered on the back side.  If the mirror is silvered on the front side you need to use cylinders or dominos on edge, etc., to check perpendicularity.
    Gary Harkins C400 #140 "Cygnus"
    Website   http://www.hometown.aol.com/htycgary/myhomepage/index.html
    Harbour Towne Marina, Muskegon, Michigan Slip C-28
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