1. Measure the horizontal distance from the base of a vertical tree (or the position directly beneath the tree tip of a leaning tree) to a location where the required point on the tree (e.g. tree tip) can be seen.
   
   
2. Sight at the required point and move the index arm over the scale until the bubble tube is level.
   
   
3. Read the percentage scale (or the degrees and minutes of the angle).
   
   
4. Calculate the height by multiplying the percentage read by the horizontal distance (or by multiplying the horizontal distance by Tan of the angle).
   
   
5. Site to the base of the tree and repeat steps 2 - 4.
   
   
6. Combine the heights from steps 4 and 5 to determine total tree height:
   • Add the 2 heights together if you looked up to the required point in step 2 and down to the base of the tree in step 5.
     
     
   • Subtract the height to the base of the tree from the height to the required point if you are on sloping ground and had to look up to both the required point and the base of the tree.
     
     
7. Check all readings and calculations.

[abney.htm] Revision: 6/2001
Cris.Brack@anu.edu.au