Surveying - Carpenter's and Builder's Math, Plans, and Specifications - page 219

The horizontal axis must be perpendicular to the vertical axis.
The attached level line and the line of collimation must be
parallel.
The zero of the vertical circle must correspond to the zero of
the vernier when the telescope is horizontal.
Adjustments of the Transit
The following sections describe the necessary adjustments of the
transit.
First Adjustment
Make the axis of the spindle vertical and the planes of the plates
perpendicular to it.
1. Set one level over a pair of plate screws. The other level will
thus be set over the other pair.
2. Level up both levels by means of the plate screws.
3. Turn the vernier plate around by a one-half revolution. If the
bubbles remain centered during the motion, the vernier plate
is in adjustment. If they have moved, bring them halfway back
by means of the adjusting screws and the rest of the way by
means of the foot screws.
4. Repeat the operation, and determine if the bubbles remain
centered when revolving the divided circle. If they do not, the
plates are not parallel, and the transit must be sent to the
manufacturer for repairs.
Second Adjustment
Collimate the telescope.
1. Set up the transit in the center of open and practically level
ground. Carefully level the instrument.
2. Drive a stake or pin approximately 200 or 300 feet away.
3. Measure the distance.
4. Take a sight on that point, and clamp the plates.
5. Revolve the telescope vertically (in altitude) by one-half a rev-
olution, thus reversing the line of sight.
6. Measure in the new direction the same distance as first mea-
sured, and drive a pin.
7. Unclamp and revolve the vernier plate by one-half a horizontal
revolution.