According to the FreeExpression source code, all the dials are PF0, PF1 and PF2 (A0, A1, A2). But no matter what I did, my test sketches came back with nothing but 0 for reading dials. What to do? Break out the multimeter.

There must be multiple revisions of the Expression V1, because the two LEFT dials (speed/pressure) are connected to PF1 and PF2, respectively. PF1...must be set high, and that results in valid ADC data from the two left dials, which I want to be...speed and pressure (adjusting feed rate and laser strength, respectively). 

One side effect of this is that the readings, while falling into specific ranges, will need to be averaged, and only change that persists over time be registered as changing values.