Next message: Bruce Stark: "Re: Perpendicularity again. was: Adjusting Central Mirror"
Alex,
This isn't an easy thing to see in one's own mind, and I doubt I could
explain it clearly. Sometimes it's easier to just do something, then figure out for
yourself why it works later on.
So please bear with me, even if you think I haven't understood what you're
saying.
Set your sextant on a table so you can get your eye down to the level of the
mirrors. A good place to set the index is about 35 degrees. That way the
horizon mirror won't be in the way. Set the vanes as I described in the other post.
For absolute precision, hold your eye about the same height above the table
as the tops of the vanes. Put the wrench in the socket behind the central
mirror and turn it one way or the other until the top edge of the vane seen in the
index mirror forms a line with the top edge of the vane seen directly.
Now the mirror is perpendicular to the frame, and I believe you'll find it
doesn't matter where you put the vanes on the arc. Nor will it matter much where
you have your eye.
Bruce
