Brother MFC9100C Service Manual page 125

(9) Loosen the screws on the eccentric bushings R and L, and then turn those bushings so that
the needles of the small dials point to the vicinity of 1 and those of the vernier dials point to
zero.
(10) Tighten the screws on the eccentric bushings.
After tightening these screws, the needles of the vernier dials may be deflected from zero.
Deflection within ±0.03 is negligible.
(11) Remove the gap reference gauge and reference jig.
IV - 84