Ultra low-tech: thread. One could conceivably let thin thread wind up around the blade's spindle during a timed run. Measure the wound string length and work

Ultra low-tech: thread. One could conceivably let thin thread wind up around the blade's spindle during a timed run. Measure the wound string length and work your way back to the RPM of the blade. Not sure how various materials (say, sewing thread vs thin vinyl fish line) would hold up at 10k RPM, but there might be something that could survive at a proper tension? EDIT: Reading fail. Someone had already commented on this. Still seems like a interesting challenge to attempt.