Diagram to illustrate points, lines, and triangles needed in measuring tree height
OBSERVATIONS:
    1. ENTS method is to measure BG of triangle ABG and DE of ADE.
    2. Clinometer only users sometimes try to form ACD and ADE.
          a. These users recognize that B is not over the trunk of the tree and consider
                the tree's true height to be CE.
    3. Other clinometer only users treat B as though it were directly in line with CE
          a. These users make large errors when BF is much closer to AH than is CE
    4. Crown point cross-triangualtion seeks to locate point F
ASSUMPTIONS:
    1. AG and AD are level with point A, so GD is level
    2. HF, HE, and FE are gound lines
PROBLEMS:
    1. Locate F, measure FE, and compute horizontal component of FE
    2. Derive useful results from these relationships
NOTE:
    1. My 8.3-foot average error calc was derived from
            a. Using angle BAG
            b. Distance AD
            c. Height = Tan(BAG) x AD
    2. Many tangent based calcs do not incorporate this error, but many do
ADDITIONAL NOTES:
1. Laying out line HFK will allow useful computations and comparisons to be made.
2. Line HK can be established with two people and a long tape measure.
    a. Person #1 directs person #2 to follow the line from H to beneath the crown point and beyond using a plumb bob.
    b. Person #2 carries a tape measure laying it on the ground and creating line HK.
    c. Locating point F can be done by computing AG and where possible stretching the tape and hold it level with Person #1's eye until F is reached. 
    d. If the point B can be seen from a sufficiently separated spot, a second tape can be run beneath B and where the  tapes cross is F
3. If F can be located relative to AH, all kinds of useful calculations can be made and relationships derived.
4. In addition to the dendrometer work and ordinary height measuring, I hope to develop a sample of 100 trees of varying species and shapes 
      for which heights have been determined and the points F located.
5.John, do you have any time in late Oct and beyond to work on this or a similar experiment?