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Attached is a plot of the errors in my lunar observations over the
past couple of weeks.  They were reduced with Frank Reed's online web
calculator.  The sextant is an Astra IIIB with 6x30 prismatic scope.

The individual sessions are outlined in beige.  The first session is
pretty much a disaster due to two things:  the telescope was
miscollimated by about two degrees, and even on top of that, I was not
properly centering the object in the telescope's field of view, not
being sufficiently aware of the criticality of doing that.  I used my
eyeglasses for this first session---the eye relief of the scope was
insufficient for me to see the edges of the field of view, and so I
ended up looking through pretty much a random segment of the field of
view.  Not good.  All subsequent sessions were without eyeglasses and
the telescope focus adjusted accordingly; the image quality suffers a
tiny bit because of about 1 diopter of astigmatism, but overall it's a
win.

After the second session, I felt I had this thing nailed, but alas, it
was not to be.  I think there are still some residual collimation
problems (I wish the scope had a reticle), and perhaps some micrometer
worm error and arc error mixed in, though that's just a guess at this
point.  I've also plotted the errors against complete angle and
against angle modulo 1 degree, and nothing really stands out.

I hope this is useful as an example of what to expect on the early end
of the learning curve.

Cheers,
Peter

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