NavList:

Alan, you wrote:
"Seems like it would involve major surgery to attach such a scope to a sextant, assuming that it could be done at all."

In case you missed my follow-up, no surgery needed! The idea here is to place the spotting scope on a tripod in line with the normal position of the sextant telescope. Since you own a spotting scope, maybe you could try it. Find some suitably distant clearly-defined edge, like a radio tower five or six miles away. Place you sextant on its side (on a table or on some support on the hood of your car or some other convenient flat surface) looking at the tower. This will be your "horizon" line for your index error test. Line it up and read off the index error. Repeat ten times and you will typically find a spread of several tenths of a minute of arc in your numbers. A standard deviation of 0.5 minutes in IC tests is not unusual. Next remove the standard telescope from the sextant. Place your spotting scope on a tripod in line with the standard telescope's former position so that the spotting scope is now looking right at the horizon mirror. Repeat the IC tests, and you should find that your standard deviation is now greatly reduced, and you can confidently assume that your IC is accurate to the nearest tenth of a minute of arc.

-FER

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