Originally Posted by FBinNY

To center, place a wheel you know to be true and centered in the stand, and clamp it in gently. Loosen both collars and tap the knob either way until the wheel centers in the caliper. Push the collars against the upright and tighten the set screws.

If you get the stand fairly close to perfectly centered, say within 1/8" leave the collars alone, and fine tune the precise centering by using the large nuts on either side of the swing arm assembly to walk the arm in either direction.