Thanks for that. I thought that was the case but its good to confirm it.
Not sure about getting it to calculate the rpm etc as then a minimum required speed of the roller would be required before it passed useful information across. 100ms being 10 revs per second or 600rpm which is about half the actual final speed, so alot of information would be missing (2000rpm would be the very maximum speed).
So in saying that perhaps i would need more than one reference point on my roller to determine the RPM. Which is easy to do.
On a side note realistically how long does it take for a Arduino Microcontroller (do they have higher clock speeds on some variants?) to read a analog or digital input and output it to a serial. 2000RPM is only 33.3HZ (30ms)
Thanks! I'm a complete newbie... I have only built one other arduino project, being a basic datalogger. But have a background in some electronics and programming!