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Clinometer (forestry)

The clinometer is a common tool used in forestry to measure slope, vertical angles, and -in combination with range measurements- elevation change or tree heights.

How it works

Clinometers, known in many fields as "inclinometers", make use of basic trigonometric principles. Multiplying the distance (D) between the observer and an object times the tangents of the angles to the base and to the top of the object, and then adding them together gives the observer the total height of the object. There are typically three different scales that can come on a clinometer: degrees, percent, and topo. When considering purchasing a clinometer it is important to be sure it is calibrated to units suitable for the intended use.

Tree height measurement

The forester stands at a fixed distance from the base of the tree. The most common distances in the United States are 50, 66, and 100 feet. To obtain accurate readings it is best to use taped measured distance instead of paced distances. For the most accurate readings it is best to use a distance that is equal to or greater than the height of the tree you are measuring. The observer sights to the top of tree, if total height is the desired measurement. If merchantable height is the desired measurement the observer sights to a point on the tree where no more merchantable timber can be used. The observer then measures to the bottom of the tree and adds the two figures together. This will be the height of the tree. Always measure a leaning tree so that the tree is leaning to the left or right. Measurements should never be taken with the tree leaning toward or away from the observer because this will affect the accuracy of the measurement.

Slope measurement

The clinometer is also commonly used by foresters to obtain the percent slope of terrain. This measurement is based on the same trigonometric principles described above. Slope measurements, however, require that both observer and target be a constant height above the ground; thus a range pole or height of measurement (HI) stick is often used in slope measurements.