A theodolite is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes.
How to set up the Theodolite
Find a smooth level of ground with a good view of where you want to spot.
Extend the legs of the tripod so that the theodolite will be at a comfortable level for you to use, splay them as far as they will go (most theodolite tripods will have a mechanism that will lock them when they reach their maximum separation and extension), and stick the ends of the legs into the earth as much as you can.
Adjust the three leveling screws on the base of the theodolite so that it is level. The spherical spirit level mounted on the theodolite will give you an idea of when it is roughly level.
Align the long spirit level with two of the three screws and readjust those two screws to achieve a more accurate level on that axis. Then turn the theodolite 90 degrees on its base and adjust again using the third screw.
Release the two horizontal adjuster clamps (usually large knobs on either side of the theodolite, slightly vertically offset).
Align the upper part of the theodolite with the mark on the ring between the two sides connected to the horizontal clamps, then lock the upper clamp.
Open the mirror light source on the side of the theodolite, and look through the small eyepiece. You will see three scales: horizontal, vertical, and fine adjustment. Use the fine adjustment knob on the upper part of the theodolite to align the mark with 0’00” (0 minutes and 0 seconds of arc).
Use the upper horizontal adjustment knob to align the single line you see in the scope on the bottom half of the horizontal scale exactly between the double lines which sit below the number 0.
Create a reference line by lining up the theodolite horizontally with a tall landmark within easy view. Unlock the lower clamp to make this rotation, line the sight up with the landmark, and lock the lower clamp again. The horizontal measurement will still be zero. From now on, only loosen the upper clamp to make horizontal adjustments.