the trimmers: one (the furthest from the power connects) is for "offset" and the inside is for "symmetry".

the BEST way to calibrate it is with a clean bipolar 10vp-p triangle as your input source and with a scope.
I realize alot of folks dont have access to a scope, so youll have to use your ears.

step 1 is adjust the offset while montoring the output. start with the 1st section. ie,
patch the test signal into in1a and monitor out1. trim the offset so that the signal is
centered a about ground (assuming an ideal test signal) next, trim the symmetry for that
section for vertical symmetry. be sure the bias control is all the way down as well as the all control.
u may have to go back and tweak the offset slightly after the symmetry. repeat for sections 2 and 3.

if you dont have a scope around, you can still get really close with your ears. there's really no
"wrong" way to set it up anyways.. the way i set them up for perfect symmetry. you can add asymmetry
with any offset at the input. so by ear, same procedure except youll be listening for odd harmonics.
the idea is to trim out any asymmetry (both pots affect this, offset to a much subtler degree,
but its audible) so start with symmetry, trim the even harmonics out as much as possible, then use offset ,
then go back if u need to. remember also that any offset at output 1 will
create a little assymetry at input 2.. so take them in order.

the trimmers shouldnt have to be tweaked very far either so if you find you gota go all the way ccw or cw with them, something is up.