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On Mon, 23 May 2005, Bill wrote:

> Interesting that your IC was zero, which matches the arc error at 0d.

Before checking the arc they SET Index error to be ZERO,
by adjusting the horizon mirror.
Zero is used as a point of reference, so arc correction
at zero is zero by DEFINITION.

> I am
> surprised the backlash problem did not show up in your IE checks.

I am also somewhat surprised. One explanation is that I
always tried to follow the Russian manual recommendation
to always rotate the screw (when touching the bodies) in one direction:-)
Including the index error checks.
The recommendation is given exactly for the purpose of
reducing the backlash effect.

On the other hand, I did try to estimate backlash myself
(with stars) and came to the conclusion that it was nonsubstantial.
So the relatively large errors in my star to star distances (like
0.3'-0.6')
remain unexplained. Fred also tried my sextant once,
the result had a similar error to my ones: about 0.3' with
art horizon.

Alex.

   

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