Levelling
The theodolite could be used for leveling provided a
number of precautions are taken.
a) The altitude bubble should be centred and the telescope locked with a
vertical angle of exactly 00-00-00,
b) Read the staff.
a) Change face and repeat the above steps
b) The mean of the two staff readings will give a reasonable result over short
distances.
Levelling by theodolite must never be regarded as an acceptable alternative to
the surveyor’s level where accuracy is needed.
Optical distance
measurement
Horizontal distances can be measured using theodolite
and leveling staff. These distances can be accurate to 0.1 m and cannot
be used where accuracy is
required.
4
Sight a vertically held leveling staff and read the staff where it is cut by
the horizontal crosswire and the two stadia hairs.
5
Check the staff readings. The difference between center and top readings
should equal difference between centre and bottom readings. Read the
staff again if there is a disagreement.
6
Note the vertical angle after levelling the altitude bubble.
7
Compute the horizontal distance from
100 xsxcos2 vertical angle
where s= difference between top and bottom stadia readings