This end and the tree bark should be in the same line. Move your eye across the stick to the right-hand edge of the tree. Be sure not to move your head, only your eye. Read the tree diameter to the nearest inch where the right side of the tree crosses the stick. The usable tree height is the second measurement used to find board foot volume.
Hypsometers are instruments foresters use to measure tree heights.
Many different types of height-measuring devices are available. The Merritt hypsometer is a linear scale imprinted on one face of the tree scale stick you used in finding tree diameters. You can use this same tree scale stick to find both your diameter and tree height. You can use a tape measure or mark a length of nonstretch string 66 feet to get this distance. With a little practice you will learn how to pace this distance.