Distortion control pretty easy really, just sequence the welds to be opposite, then when its finished a tap with the knockometer to make sure the arms are in line, all the arms are internally vented, with the vent holes feeding back to a final hole concealed under one of the castor plates.
Its a STEL up200i, AC DC, pulse, frequency control & square wave, a few years old now but brilliant machine, BOC used to sell them under the transtig name, exactly the same as this.
Never use a pedal, last machine I used with a pedal was a BOC ADR years ago, sometimes use a remote footswitch instead of the torch button, most of my jobs are off the bench so a pedal's not much use.