- Find a tree surrounded by level ground. Hold a yardstick as shown; the distance between the top of the yardstick and your hand should be the same as between your hand and your eye. Keep the stick perpendicular to the ground and sight straight in front of you so the top of your hand appears to be even with the base of the tree.
- Keeping the tree base aligned in this way, walk backward and, moving only your eyes if possible, look over the top of the yardstick until it appears to be even with the top of the tree. Use the string and the yardstick to measure the distance between you and the tree trunk; that distance equals the approximate tree height.
- Why it works: By holding the yardstick in this manner, you form a small right isosceles triangle (a triangle with 2 equal sides and a right angle). You also create a larger triangle with identical proportions whose 2 equal sides are your distance from the tree and the tree's height (see diagram). Adding the height of the child doing the measuring to the final tree height will make your estimate even more accurate.
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