The best trade-off for resolution v. price I can think of is an optical mouse. At <USD10 and 400 ticks/inch it's not too shabby (are there higher res OM out there?).
A 3.1416 inch diameter disk produces 4,000 counts/revolution at the perimeter. That's 11.11 counts/degree or about 5.4 arc-min/count (if my arithmetic is any good).
Even though that's only 1/25 of the goal of 100k counts/rev the price is attractive.
robotic regards,
Tom
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"We have civil engineers; too bad we can't engineer civility."
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