PID Velocity Control

[j.cole]

The intended operation is to get the RPM of the motor. Now what I expected to happen was that every half a second the program would take the current value and write it to the previous value. And then take the previous value and subtract it from the current value. Giving me my total rotations for that half second.
I've never used shift registers because I have no understanding of them at all and it was easier to do it a different way than learn something, which I should have done in the first place. 5 weeks in is a little bit late eh?