BARTINGTON INSTRUMENTS
Page 17 of 32 OM2020/5
2. Rotate the telescope to a horizontal position with the probe at the top and apply the vertical
clamp. Release the horizontal clamp and align the tubular level between any two foot-screws
A and B. Foot screws A and B should be turned in opposite directions by equal amounts until
the tubular level is centred.
3. Rotate the Theodolite clockwise by 90 degrees to align the tubular level with the third foot-
screw C, and adjust the level in that direction using foot-screw C. Rotate 180 degrees and
reduce any error by half, again using foot-screw C.
4. Rotate theodolite by 90 degrees clockwise. Note the position of the tubular level bubble.
Bring the bubble to a halfway position between this position and a centred position by turning
foot screws A and B by equal and opposite rotations.
5. Rotate theodolite by 90 degrees clockwise. Turning foot screw C bring the bubble to its mean
(halfway position).
6. Check that the bubble now remains in its mean position through full rotation.
7. Repeat the above steps as necessary, centring on the mean position until it remains stable.
6.2.2. Setting Over A Reference Point (Tripod Mounted)
1. Position the tripod (if used) over the ground reference point with its head level. Mount the
theodolite and level the instrument using the circular plate level and foot-screws.
2. To focus the optical plummet (tripod only) on the graticule, turn the eyepiece and focus on the
ground point by pulling or pushing the eyepiece tube. Line up the graticule and target point
by adjusting the tripod legs and/or instrument foot-screws as necessary.
3. Re-level the instrument with the foot-screws and complete fine centring by moving the
instrument on the tripod head. If necessary, repeat levelling and centring procedure until
instrument is level, directly over the ground point.
6.2.3. Setting Over A Reference Point (Pillar Mounted)
When siting the theodolite on a pillar, the procedure is similar to that in the previous; however,
when pillar mounted, the optical plummet would not be used and the pillar mounting plate would
be fitted to the theodolite.
Use the tubular plate level to level the theodolite to better than ±15”. Each 2mm interval
represents 30” error. If this cannot be achieved then there is a problem in the setting of the
tubular level. This error can be completely eliminated using an adjuster pin as follows.
1. Attempt to level with tubular level set in line with a pair of levelling screws.
2. Rotate to the next pair of levelling screws. Remove half the error using the tubular level
adjuster and half the error using both the level adjustment screws.
