# How to make a theodolite

Written by john woloch
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What goes up must come down, but sometimes what goes up stays there long enough for you to measure its height. A theodolite is a simple device for doing exactly that: measuring the height of objects like trees and even model rocket flights. A theodolite measures the angle formed by the elevation of a tree, for example, and the point on the ground at which you make your measurement with the theodolite. Using trigonometry -- the tangent of the angle you measure will equal the height of the tree divided by your distance from the base of the tree -- you can find the height of the tree.

Skill level:
Easy

### Things you need

• Plastic protractor
• Rectangular piece of cardboard at least as long as the protractor
• 3.8 cm (1 1/2 inch) finishing nail
• Small binder clip
• Cotton
• 226 g (1/2 oz) fishing weight

## Instructions

1. 1

Place a plastic protractor on a rectangular piece of cardboard so that the straight edge of the protractor lines up with the long edge of the piece of cardboard (see Resources).

2. 2

Push a 3.8 cm (1 1/2 inch) finishing nail through the small hole in the base of the protractor. Keep pushing until the nail pierces the piece of cardboard behind the protractor.

3. 3

Push the nail until 1.3 cm (1/2-inch) of the nail is protruding through the cardboard.

4. 4

Secure the end of the finishing nail with a binder clip by placing the clip over the end of the nail that's protruding from the cardboard side of your theodolite; this will hold it in place.

5. 5

Tie a 30 cm (12 inch) piece of cotton to the finishing nail on the protractor side of your theodolite.

6. 6

Tie a 226 g (1/2 oz) fishing weight to the other end of the 30 cm (12 inch) piece of thread.

7. 7

Note that the thread of your theodolite now indicates anglural measurements on the protractor when you tilt the theodolite.

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