How to record the number of revolutions a continuous servo has done...

How to record the number of revolutions a continuous servo has done in some time interval? I was thinking it may be done using 2 arrays, one for time and the other for the servo position, but I was wondering if someone else has something else?

Edit: Basically, how to measure rotational velocity?

Hall Effect switch.

I was thinking it may be done using 2 arrays, one for time and the other for the servo position

The time of what? How do you propose to get servo position? The variable-speed-reversible-electric-motor-that-is-NOT-a-servo has no means of knowing anything about position.

You need an external position sensing device - for example, as @AWOL has suggested a magnet attached to the servo and a hall-effect sensor to detect every time the magnet passes it.

If you need more sophisticated control you could use a rotary encoder - but that will make the programming more complex - especially if the servo rotates at high speed.

...R

If you are really good at modifying servos, you might modify the servo for continuous rotation using resistors in place of the internal pot, and then read the values coming from the still attached internal pot. The pots in servos I have modified do not have stops and will freely rotate. The stop in the servo is a tab on the output gear.