The Really, Really Basics of Laser Rangefinder/Clinometer Tree Height Measurements http://www.nativetreesociety.org/measure/really_basic_3a.pdf
Many of us have been measuring tree heights for a long time. We have subconsciously incorporated subtle details of the process into our routine. We have filed away much of what we have learned as obvious. There are steps we go through without even thinking about the mechanics of what we are doing. On the surface of everything, the process seems simple and it is if you know what you are doing. Essentially we measure the straight-line distance to the top of a tree using a laser rangefinder. Then we measure the angle to the top of the tree with a clinometer. The height above eye level is calculated using a pocket calculator to be the trigonometric sine of the clinometer reading x the distance measured to the top of the tree. The same process is used to measure how far the base of the tree extends vertically above or below eye level. Then the number for the height of the base of the tree above or below eye level is added or subtracted from the number for the top of the tree to get the total height of the tree. If we able to show someone in person how to measure a tree, we can do a fairly adequate job of it. But for people just learning the techniques on their own, it isn't as straight forward and trying to explain the process through emails, through online chats, or even through an article is a much more hit or miss proposition. This is not only because of the math involved, but because of the variability in the shapes of the trees and the obstacles to seeing their tops and base from a common vantage point. Actual field situations add levels of complexity to tree measuring beyond that of the theoretical models taught in forestry courses. This article goes over the very basics of how to use a clinometer, a rangefinder, how to do the measurements, and even the procedure for using the trig function on the calculator to calculate tree heights.
"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky