Take your height off the ground (treestand height) square that, take the length to the deer from the base of the treestand, square that, add the two numbers together, and that equals the actaul distance from you to the deer squared, you will need to find the square root from that, and then u have the measurement in whatever unit of measurement you used., I dunno if being higher up in the airmakes the arrow drop anymore or what not, but thats the formula you use for pythagorean theorem (A^2+B^2=C^2), and it is for the hypotenuse of a triangle, which is exactly the same thing as the triangle your treestand, deer, and distance on the ground makes up. I could be wrong, but I tried to remember all that off the top of my head so don't mark me by my words.