What is a rangefinder?

What is a rangefinder?
Rangefinder is a tool for measuring length or distance, and can be combined with angle measuring equipment or modules to measure angle, area and other parameters. There are many forms of rangefinders, usually a long cylinder, which consists of an objective lens, an eyepiece, a display device (can be built-in), and a battery.
Rangefinder refers to a radio navigation device that measures the slant distance between an aircraft and a ground responding station. It consists of an airborne interrogator and a ground answering station. The method of determining the distance between the two by measuring the time required for the round-trip of the radio wave from the plane to the radio. Aviation uses pulse waves near 1000MHz to inquire and answer, with a range of about 500km, for use on air routes. In addition, in order to cooperate with the microwave landing system when approaching and landing, a precision rangefinder has been developed, which uses the waveform of the pulse front with a faster ascent rate to improve the accuracy. Its operating distance is about 40km. The working frequency of the two rangefinders is the same and can work compatible.