RPM Measurement Using a Microcontroller - The LM2907 Technique

A robust way to measure RPM using a technique modeled after the LM2907 frequency to voltage converter. I like this technique for the following reasons:
It uses regularly spaced, clock generated interrupts.
There are no division operations that could lead to a divide by zero error.
There are no subtraction operations that could lead to sign errors.
It is robust to noise such as contact bounce.
It naturally filters out high frequency noise in the signal.
It does not require an analog input.
The code is very compact; although, it does require floating point math.