- controls the speed/rate of the LFO wave that controls the effect
- controls the depth/amplitude of the modulation (the size of the range in which the effect sweeps).
- sets the amount of effected signal fed back into the effect (for a stronger effect)
Gerd Schulte Audio Electronik Compact Phasing A
used by Kraftwerk
Here's some code to post a link with image on forums, eBay, websites,...