Calculating quadratic mean diameter, a conventional measure of the average tree diameter in a stand, requires estimates of the stand's basal area per acre and trees per acre. Basal area per acre, a measure of the stand's stock, consists of the average of the sum of the cross-sectional area of all of the trees taken at 4 1/2 feet above ground level.
Press "(" on the calculator.
Press "(" again then enter the basal area per acre figure.
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Press "/" then the trees per acre figure followed by ")."
Press "/" again and enter "0.005454." Press ")."
Press the "x to the power of y" key, an italic "x" with "y" in superscript above it.
Enter "0.5" and press the equals button. The display will show the quadratic mean diameter in inches, the traditional measurement used.
Quadratic mean diameter equals ( [BAPA/TPA] / 0.005454) to the power of 0.5.