How to Measure Angles Using a Theodolite
A theodolite is an instrument used commonly by builders and engineers to measure precise angles, which is necessary for large scale construction projects. A basic modern optical theodolite typically consists of a small telescope which is connected to two angle measuring mechanisms, one for measuring horizontal angles and one for measuring vertical angles. It sits atop a rotatable base with a leveling mechanism on a tripod. Once the theodolite is set up, the telescope is turned to spot the desired point and then the angle from the point that the theodolite is placed to the point spotted in its telescope can be read through the eyepiece of the scope.
Setting up the theodolite
Step 1
Find a patch of firm level ground with a good view of what you wish to spot.
Step 2
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.
Step 3
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.
Step 4
Align the long spirit level with two of the three screws and readjust with 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.
Step 5
Release the two horizontal adjuster clamps (usually large knobs on either side of the theodolite, slightly vertically offset).
Step 6
Align the upper part of the theodolite with the mark on the ring between the two sides which are connected to the horizontal clamps, then lock the upper clamp.
Step 7
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).
Step 8
Align the long spirit level with two of the three screws and readjust with 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.
Step 9
Release the two horizontal adjuster clamps (usually large knobs on either side of the theodolite, slightly vertically offset).
Step 10
Align the upper part of the theodolite with the mark on the ring between the two sides which are connected to the horizontal clamps, then lock the upper clamp.
Step 11
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).