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Bill, you wrote:
"as well as producing a circle to mount on the eye end of the scope
with a tiny hole to be sure I am shooting down the center of the
scope."

Do you need that? I never did anything like that in my tests.

And you wrote:
"When matching the predetermined mirror distance, the sextant reading
was just a hair below 0.8' on the arc."

Sounds good. Try this:
Set the sextant micrometer to 0.0'. Fire up the laser, and carefully
measure the distance between the dots (lines) at 20 feet distance with
an ordinary pair of drafting dividers. Record by pressing the divider
points into an index card. Now set the micrometer to 1.0' and do it
again. Record the second measurement the same way, but use the same
indentation in the index card for one point of the dividers. Then
repeat both measurements at 40 feet. If you do this right, on your card
you should have one small indentation on the left as the starting point
for each measurement and then two indentations closely spaced three or
four inches to the right (from the 20 foot observations). Just below
those, you'll have another pair of indentations (from the 40 foot
observations). The spacing between those marks should be almost exactly
twice the spacing between the upper indentations. That much is obvious,
but there's more. If the index error is exactly 1.0 minutes, the two
indentations furthest to the right will be exactly above each other
(the same distance from the far left indentation on the card), while
the other pair of indentations will be skewed (a line drawn them would
not be perpendicular to a line drawn to the far left mark). Note that
this is simply a paper method of recording the exact distances between
the laser beams at 20 feet and 40 feet. The whole point is that the
distances between the beams will be exactly the same when the sextant
is set to the correct index error because the beams are then exactly
parallel.

By the way, if you can't find a larger indoor area, and if the Ice Age
has arrived and pleasant weather never returns, there is another
option. Find an optically flat mirror (or two) that's large enough to
intercept both of the dots from the laser. You can bounce the beams
back across your room doubling the available space. Optical flats are
expensive, but sometimes they turn up cheap as surplus telescope
components. The secondary mirrors of Newtonian reflecting telecopes are
usually high-quality optically flat mirrors. Or you can just tough it
out and enjoy this fine Siberian weather we're having.

-FER


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