How to make a theodolite

Written by john woloch
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How to make a theodolite
Make a simple theodolite to learn the height of the trees in your garden. ( Images)

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:

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

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  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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