When you cut down a tree, its inclination will affect where it will fall. There is a lot of frightening movies where they end up in the wrong place. You should really figure out the inclination before starting the chainsaw. You could now do that in the latest update of Arboreal Tree Height on iOS. In the latest update you get the perpendicular height, inclination and tree length.

There is also a problem when trying to measure the actual height of a tree if it is inclined. If the tree is leaning too the sides, the tree is always longer than the perpendicular height. The affect is not so large. An inclination of 10 % only makes the tree 1.5 % longer.

There is also a problem when trying to measure the actual height of a tree if it is inclined. If the tree is leaning too the sides, the tree is always longer than the perpendicular height. The affect is not so large. An inclination of 10 % only makes the tree 1.5 % longer.

The largest error appears when measuring a tree that are leaning towards or away from you. You will then get an incorrect angle and result. If the tree is leaning away from you as in the image above, you will get an underestimation of the length of the tree. The image is from the website AWF-Wiki.

If you want get a correct measurement of a single tree you should measure the tree from two sides, perpendicular to each other. Choose the height from the side that has the greatest inclination

If you are measuring many trees you could suppose that they are leaning in different directions and that the mean height will be correct.