
Tools for measuring tree diameter Forest Measurement and Modelling. 

Fiberglass tape: A girth tape measures diameter indirectly. The tape is wrapped around the tree to measure circumference. This value is divided by PI (3.1415....) to estimate diameter. Often the tape will have normal units (mm and cm) on one side and PI units on the other side. 

Calipers: Calipers are comprised of a fixed arm, scale and moveable arm. The fixed arm is placed along one side of the tree at the desired height. The moveable arm is then placed flush against the other side of the tree and the scale is read directly. The calipers must be located perpendicular to the stem axis. 

Spiegel Relaskop (Relascope): Commonly referred to as a Relaskop. A sophisticated, compact and robust device for measuring range, tree height and diameter, and stand parameters. It is relatively expensive. 

Telerelaskop: A research quality instrument that is no longer in production. The Telereskop is similar in principle to the [Relaskop] except that it includes 5 x optical magnification. 

Criterion Laser: A heavy height, diameter and range measuring instrument. The Criterion uses laser light to determine distance from a tree. The user enters numbers read from a riflescope and a simple computer chip calculates diameter. 

Pentaprism: A medium weight and cost instrument for measuring tree diameter. The Pentaprism uses a moveable prism to superimpose an image of the tree bole over an original image. When the sides of the superimposed image line up with the original image, the diameter can be read directly from a scale which measures displacement of the moveable prism. 

Ranking tools for ease, effectiveness and cost 
I have ranked the above tools used for measuring diameter at heights not within easy reach. My interpretation of 5 main factors:
 

[toolsd.htm] Revision: 6/1999 