The term hypsometer comes from two Greek words meaning "altitude meter" and typically refers to a device that is used to measure the height of an object. There are 3 types of hypsometer: scale, pressure, and laser. The device is commonly used in surveying and construction industries as well as by arborists, who use hypsometers to measure heights of trees.
The scale hypsometer is the simplest form of this device. It consists of an L-shaped frame with a plumb or level and an adjustable straightedge. The user sights the top of the object using the straightedge and notes the angle formed between the bottom of the frame and the straightedge. Employing a formula from trigonometry, the user can calculate the height of a building or other structure.
One also can use a yardstick as a scale hypsometer. Standing 25 feet (about 7.5 meters) from an object and holding the yardstick about 25 inches (about 64 centimeters) from one’s eye with the "0" at the bottom and aligned with the base of the tree or structure, one can note where the top of the structure corresponds to the marking on the yardstick. 1 inch (about 2.5 centimeters) on the yardstick equals 1 foot (about 0.3 meters) in height.
A pressure hypsometer utilizes the principle that the boiling point of a liquid decreases as height increases. It is constructed using a reservoir filled with liquid, typically water; a heating mechanism; and a thermometer. By comparing the temperature at which the water boils to a data table, one can determine the height of the structure. The device is somewhat impractical for casual use; it requires using the hypsometer at the top of the object being measured and the height of that object being significant enough to yield an observable temperature difference in the boiling point.
Arborists are the typical users of the laser hypsometer. These portable, computer-equipped devices use emitted and reflected laser light to measure and perform the calculations. The device measures the amount of time required for the beam to be returned to it; using that data along with sensors to determine angle, it calculates the height of the tree. It can also measure the diameter of the tree and calculate how much wood the tree will yield.
The hypsometer may be used by other professionals as well. Surveyors may use the pressure variety to determine the height above sea level of a parcel of land, for example. Maintenance and construction personnel can also use either the scale or laser varieties of the device to assist in determining needs for materials or labor.