How to adjust the optical plummet on a leica survey tribrach ?

The 4 adjustment screws hold the reticule lens in place. Two screws (on opposite end) control left to right and up and down. They are located usually under a ring that screws out, that is attached to the objective focus on the plummet.

A special jig is used by the technician to mount the tribrac so the plummet faces up, and spins on an axis with leveling screws. In a pinch, a second tribrac and a puck the same size as the inside of the tribrac that is tall enough to fit in the "tool" tribrac on bottom, and the tribrac to be ajusted on top and allow the top to spin without hitting the bottom tribrac.
A fixed point is established and centered on, by moving the foot screws on the bottom tribrac to tilt the top tribrac. Then the top tribrac is rotated 180 degrees and the fixed point is observed again. If the reticule is no longer on the point then half the error is taken out using the 4 adjustment screws and the other half is taken out using the foot screws on the bottom tribrac. This step is repeated until the top tribrac can be rotated 360 and not move off the fixed point.