Hypsometer

Hypsometer is a surveying instrument used to measure the height or altitude of objects or terrain. The name derives from the Greek hypsos, height, and metron, measure. In its classical form, a hypsometer determines height by combining a measured horizontal distance with the angle of elevation to the top of the object. If the observer's eye height is known, the height can be computed as h = d × tan(θ) + h0, where d is the distance to the base and θ is the angle of elevation.

Some hypsometer designs use a fixed baseline with a sighting telescope so that aligning the top of the object with a graduated scale yields a direct height reading, effectively providing a direct measurement without separate trig calculations. Other variants employ two sights separated by a fixed vertical distance to obtain a direct height reading when the line of sight matches the top of the object.

Hypsometers were used in surveying, architecture, astronomy, and forestry, notably for estimating tree heights in the field. They can be simple and portable or more elaborate, with telescopes and compensating mechanisms to reduce parallax and refraction errors.

With the rise of digital instruments, including theodolites, electronic clinometers, and laser rangefinders, traditional hypsometers have become less common in professional practice, though the term remains in historical references and is still used in some forestry surveys and education.