How to work out the rotation speed of a bike wheel.

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3

Thanks for that!
Im running my simulator in Virtual Breadboard, and it doesn't accept a couple commands.

attachInterrupt(0, rpm_fun, RISING); -- im guessing that because i don't have any input ?

and

rpm = 30 * 1000 / (millis() - timeold) * rpmcount; - error, type 'long' is not assignable as a 'int'