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At 06:04 PM 10/11/04 -0500, eremenko@MATH.PURDUE.EDU  wrote:
>Dear Bruce,
>I am very glad to the opportunity to repeat my question again
>(The question was addressed to everyone who EVER checked
>perpendicularity of the index mirror,
>but surprisingly nobody replied when I asked it
>for the first time about a month ago).
>This has nothing to do with SNO-T sextants or adjusting.
>
>The question was: how do you properly CHECK perpendicularity
>of the index mirror to the sextant frame.
>
>I was asking a reply of ANYONE WHO HAS ACTUALLY DONE
>this check on his/her sextant
>(and nobody replied, which is surprising).
>
>There are several versions of this check.
>The simplest one and most common one says:
>look into your index mirror so that you see a part of the arc
>directly
>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.
>
>But whether this is so or not, DEPENDS on the angle of your
>sight
>with respect to the plane of the sextant frame!
>I just cannot believe that nobody has noticed this.
>
>In other words: you can move your eye (or the sextant) so that
>the point, where the direct and reflected images of the arc meet,
>moves along the right vertical edge of the index mirror.
>You cannot get a match of these arcs at every point of this
>vertical edge. Either they match at the lower point of the edge of the
>mirror,
>or in the upper point of this edge  or somewhere in the middle.
>But never everywhere.
>
>This does not depend on the particular sextant.
>Every sextant with sufficiently large mirrors will
>behave like this (and this can be shown mathematically).
>
>So WHERE exactly should you place your eye with respect to the frame
>for the proper test?
>
>No manual says this precisely.
>
>Alex.

Mine matches top to bottom.

   

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