Clinometer Tree Height (Percent-Slope)
Tree height from a clinometer's percent scale: standing a horizontal distance D from the trunk, read the percent slope to the top and to the base, both signed (+ above eye, - below); H = D x (top% - base%)/100. At 100 ft with a +58% top and a -4% base (base below eye) the tree is 62 ft. When the base is below eye its height adds; uphill above eye it subtracts. Percent = 100 tan(angle) for a degree scale. A field estimate; lean and a hidden top add error.
Formula and source
H = D x (top% - base%)/100, D the horizontal distance and top%/base% the signed percent-slope clinometer readings (+ above eye level, - below). above_eye = D x top%/100; below_eye = D x base%/100. Percent = 100 x tan(angle).
Standard forest mensuration / hypsometry (percent-slope clinometer method), USDA Forest Service practice, by name.
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