Optional 1 or 2 fingers it doesn't matter (be honest which you use though) or be like me and post both!
Surprisingly my speed didn't double, but obviously 2 fingers was faster. (I used one finger on each hand, not 2 on one)
Use whatever test ya want, this was the first one I found; you do it 3 times in a row to get your average score. Divide the number by 10 to get taps per second.
(2 fingers, wasn't going to do one with 2 in this thread hence the time difference but figured it'd show the higher tap speeds some people claim of 10+/second)
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(Tapping with thumb alone)
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That all being said, I can't tap faster than 5/sec in FT without actually losing more taps (at 7/sec only 3-4 register tested with armor spell)