Mirrors to measure height?

8th graders are currently studying similar shapes and proportional reasoning in math class. For their hands-on project, students needed to use their knowledge of similar triangles and proportional reasoning to indirectly measure the height of objects that are too tall to measure easily by hand. Armed with a mirror and a tape measure, students measured the heights of such things as an exterior building wall and the height of the gymnasium ceiling. "Later on, we will discuss topics such as percent error and what sources of error might be," said their teacher Mr. Miyasaki.