How to Use a Surveyor's Theodolite

A theodolite is a surveyor's tool for measuring angles.

A surveyor's theodolite is used to measure horizontal and vertical angles. These measurements are used to plot boundary lines, building foundations and utility routing. A theodolite measures distance manually by chains of standardized length or metal measuring tapes along the length of the desired angle. Land-surveying students use a theodolite as a way to learn the principles of angle measurement. Surveying on the job requires the use of more-advanced surveying instruments.

Things You'll Need

• Survey nail
• Survey tripod

Instructions

1. Drive a surveyor's nail into the ground at the point where you want to set up the theodolite. Angles will be measured from this point, as will distances.

2. Set up the tripod legs, taking care to set the height where the instrument sight will be at a comfortable eye level. Be certain to check that the hole in the center of the mounting plate is located over the nail. Press each leg into the ground by stepping on the bracket at the bottom of each leg.

3. Fine-tune the position of the legs so that the mounting plate on the top of the tripod is as eye-level as possible.

4. Remove the theodolite from the case. Most theodolites have a sturdy handle on top. This is the best place to lift the instrument. Gently place the instrument on the mounting plate and screw in the mounting knob beneath the instrument.

5. Adjust the theodolite to level by adjusting the tripod legs, using the bull's-eye level. Fine-tune the adjustment with the leveling knobs on the instrument.

6. Adjust the small sight, called the vertical plummet, at the bottom of the theodolite. This sight allows you to make certain the instrument is centered directly over the nail. Fine-tune the vertical plummet by adjusting the knobs on the bottom of the theodolite.

7. Look through the main scope and aim the crosshairs at the point to be measured. Twist the locking knobs to hold the theodolite in position on the exact point. View the horizontal and vertical angles in the viewing scope on the side of the instrument.

Tips & Warnings

• To fully understand the use of surveying instruments, take a course from a licensed surveyor. The hands-on experience is invaluable in understanding the more abstract concepts associated with mathematics and instrument operation.

• Use care when transporting and operating the theodolite. These precise measuring devices are very sensitive, and they are expensive to repair if damaged.

References

• "Elementary Surveying, An Introduction to Geomatics"; Charles D. Ghilani and Paul R. Wolf; 2008