NavList:

Dear Stan,
Congratulations with your new sextant.
It looks like a very fine piece from your description.

> 1) What are the eyepiece filters for?

The eyepiece filters are for determining the Index Error from Sun
and Moon. You do not use ordinary filters. The reason is that your 
ordinary filters may have some prizmaticity, and elemination of them
permits you to determine the true Index error. (The possible prizmaticity
of the eyepiece filter has no influence). This also permits you
to determine whether there is any prizmaticity in the ordinary filters.
Also: usually the horizon filters are different from the index filters.
The eyepiece filter permits to to achieve EXACTLY the same illumination
of the two images of the Sun which is very good for determining Index 
Error.  This is the first I have heard of this.  Interesting, but it seems to me that you would want to measure the index error in the configuration you are going to use to take sights, no?

> 2) I'm having a heck of a time trying to read the vernier scale.

This requires some practice. And even with practice this is much slower
than reading a drum. This was the reason why they replaced vernier scales 
with drums in the second half of XX century, though the vernier scales
have several other advantages.  Although I have had access to vernier sextants in the past, I have always sanely chosen to use micrometer drum types.  

The magnifier works
but it seems that when I have it in a position to read the scale
it blocks the light, making it difficult to read the scale.
There is a diffuser screen that I imagine is supposed to help, but how?

You turn in such a way that diffuser screen faces the Sun, and incline
the sextant so that the Sun rays can penetrate obliquely
(through the diffuser glass) between the
scale and edge of the magnifier. Requires a little practice.  Yes, and you are right about practice.  I have been using it with sunlight illumination, and have found that if I hold the sextant at just the right angle (diffuser with respect to sun) I can see the scales better and have been getting better at reading it.

It is harder with stars. As I understand your sextant has no illumination.
You need a little flashlight (Celestaire has an excellent one) with which
you iluminate the scale when you read it.  I have been playing with a red LED indoors.  Not as easy as in sunlight, but, again, holding it at the correct angle with respect to the diffuser helps a lot.

> figuring out which of 50 vernier lines aligns with one on the arc
> seems daunting.

Yes! But after some practice this becomes easier: you learn to figure out 
quickly, which part of the vernier to look at (tzhe part where the vernier
divisions "switch the side with respect to the scale divisions".
Then you look very carefully at this place, to see which division is
best alligned.  I understand the part about switching sides, but I still am finding it difficult.  Practice, practice, practice.

I suppose yours is a 10" scale, of 6 1/2 inches radius.  Exactly.  Have you been peeking?

> 3) The sextant does not seem to have any adjustments
> with holes where the "pick" tool would be used.

Do not the mirror adjustment screws have holes for this pick tool?
Or they are threaded for adjustment with fingers?  Just finger adjustments.

It will help if you show some detailed photos.  A few photos attached.

Alex.

Stan