Relascope
The relascope, invented by Walter Bitterlich, is a versatile forest-inventory tool used mainly to measure a tree’s height, its diameter along the trunk, and the tree’s basal area for variable-radius plots.
How it works: you look through a front window. The top half shows the tree, while the bottom half shows measurement scales. There are three height scales, five diameter scales, and two basal-area scales, chosen based on distance and the desired basal-area factor. It’s similar to an angle gauge or wedge prism in estimating basal area from a point, but it has multiple functions in one instrument. It also helps account for slope, which can make measurements more accurate. The device can even be used to estimate distance to a tree (range) using trigonometry, though this is not common because it takes time.
Height measurement: the relascope uses weighted wheels that spin as you move, giving a height reading based on your distance from the tree. Common distances are 66 or 120 feet. To measure, you aim at the top of the tree (or the highest point on the bole) and read the height value, then read a second value from the bottom. Subtract the two numbers to get the tree height, similar to how a clinometer works.
Point sampling: for plot sampling, you use the relascope’s lines to decide if a tree is IN or OUT. If a tree fills the space between the lines, it’s IN and counts for basal area. The basal area is the number of IN trees times the basal-area factor (based on the gauge width).
Modern note: there is an electronic laser version called the tele-relascope, which works better in low light.
This page was last edited on 2 February 2026, at 20:15 (CET).