Would that be 60000 RPM witha 2-bladed prop or 60000 "passes of something" per minute infront of the sensor (i.e. 30000RPM for a 4-bladed prop)?
Sorry, I missed the blades calculation, my calculation was with the passes. So you get up to approx. 60000 passes per minute but at that level you loose a lot of precision with that code although that's completely unnecessary.