Telemeter
![An expendable dropsonde used to capture weather data. The telemetry consists of sensors for pressure, temperature, and humidity and a wireless transmitter to return the captured data to an aircraft.](/Images/godic/202502/15/Dropsonde_U.S._Air_Force5352.jpeg")
The original meaning of telemeter, and still one of the main uses of the word, was a device used to measure distances to remote objects, that is, a rangefinder. Originally optical devices used in surveying, they soon found military applications in rangefinding, especially naval gunnery.