source : Image by Edfrank01, distributed under a CC BY-SA 3.0 (Wiki)

Stick method for tree height measurement is simple to follow even for amateurs. It works on the principle of ‘similar triangles’ that essentially have equal corresponding angles and proportional corresponding sides. The observer holds a stick from a distance such that the top and the base of the stick align with the top and the base of the tree, respectively. Based on the length of the stick, distance  between the tree and observer, & distance between stick and the observer, tree height can be calculated. The measurement method however is prone to errors associated with exact alignment of stick with the tree and measurement of distance between tree and the observer.