Long time commercial timber cruiser, Pacific Northwest here. I did things to get good results and save time. Go out to where you can see the point you want to measure to. Use the percent side of the clino. Distance up plus negative distance down. Add that together. Say. You are 79 feet away from the tree, horizontal. 93 up, 7 down. It's equals 100. multiply by distance. .79. The tree is 73 feet tall. Or get a lazer.
Much too complicated just use a pencil and multiply how many times it will fit to the top of the tree at arms length. times a known height at the bottom of the tree for instance a six-foot person. Accurate within 5%