Draw a vertical line about 5 inches long on the piece of paper. Draw a 5-inch horizontal line extending to the right from the bottom of the vertical line. Connect the ends of the two lines to form a right triangle.
Stand on top of the sand dune. Hold the end of the measuring tape on the ground at the highest point. Ask somebody else to walk down to the base of the dune while holding the other end of the measuring tape. Make sure to keep the measuring tape straight. If you can't manage this due to where you are standing, move closer to the edge of the dune, but keep your end of the measuring tape level with the highest point of the dune. Write the distance measured by the measuring tape next to the hypotenuse, the diagonal line, of your triangle.
Hold your end of the measuring tape in the same place and ask the person holding the other end to raise his end until it is level with yours. Keep the measuring tape taut and use the level to make sure that it is perfectly flat. Use a ladder if your companion needs to move the measuring tape higher than he can reach. Record the measurement read on the tape at the point directly above the spot where you took your first measurement. Write this number on the bottom line of your triangle.
Use Pythagoras's theorem (a^2 + b^2 = c^2) to calculate the final side of your triangle, equal to the height of the dune. Multiply the distance of the hypotenuse by itself and write down the result (c^2). Multiply the distance of the base of your triangle by itself and subtract this number from c^2. Enter this number into your calculator and press the square-root button. This button looks like a check mark with a horizontal line extending from the top of it. The resulting number after pressing the square-root button is the height of the sand dune.
