According to HC reviews, the trim pots control Compression and Effect Strength.
The problem is, I can't actually work out how to get to the circuit board! I've taken the bottom of the epdal off and the circuit board is in a little plastic box that I can't figure out how to get into!
I'll keep trying though, because, apparently, the trimpots allow quite a lot of 'tweak' to be done to the tone of the pedal :)