Leonardo da Vinci designed a clinometer with a plumb line to measure vertical angles.
A clinometer, also called an inclinometer, measures the angle of elevation or slope relative to the horizontal. Leonardo’s version used a graduated scale and a hanging plumb line. Gravity kept the line vertical while the observer aimed the instrument at a feature, allowing the angle to be read from the scale.
The instrument could help estimate the height of towers, buildings, or other distant objects when combined with a measured horizontal distance. It belongs to Leonardo’s broader studies of surveying, geometry, architecture, and military engineering.
A clinometer is different from a compass, which indicates horizontal direction, and from a sextant, which measures angular separation between objects, especially in navigation. Leonardo’s instrument was a design for practical measurement; the surviving drawing does not show that he invented the general principle of using a plumb line for angle measurement.