NavList:

Alex, you wrote:
"Could you give more detail? What 30x scope, and how do you attach it to a
sextant?"

It's amazingly simple (considering all the energy we devoted to this topic over the years). You just place your sextant on its side on a table. Shim it up so that you can see centered in the field of view some distant sharp line like a tower five miles or more away from you. Then remove the sextant telescope. Get an ordinary spotting scope with magnification generally in the range of 30x to 40x. Place the spotting scope on a tripod (or on some support on the table) and place it in line with the usual location of the sextant's telescope. There's no need to attach it. Then you look through and because of the magnification the slightest motion of the micrometer yields a visible shift between the direct and reflected image of your distant target. You can now easily experiment with the various factors that affect index correction. For example, you can measure IC for clockwise and counter-clockwise motions of the micrometer drum. Again, with a decent sextant, the repeatability is excellent. Any brand of spotting scope with reasonable optical quality will serve. I bought one on eBay for around $50. You could even use a backyard astronomical telescope, but there are some issues that arise. Besides a spotting scope is a nice tool to have around.

-FER

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