Height finder

A height finder is a ground-based aircraft altitude measuring device.

Early height finders were optical range finder devices combined with simple mechanical computers, while later systems migrated to radar devices.

[1] In World War II, a height finder was an optical rangefinder used to determine the altitude of an aircraft (actually the slant range from the emplacement which was combined with the angle of sight, in a mechanical computer, to produce altitude), used to direct anti-aircraft guns.

[citation needed] Height finding radars of the 1960s and 70s were distinguished by their antenna being tall, but narrow.

As beam shape is a function of antenna shape, the height finder beam was flat and wide horizontally (i.e., not very good at determining bearing to the target), but very thin vertically, allowing accurate measurement of elevation angle, thus altitude.