Gun chronograph

A projectile passing through a screen would break one or more threads, the broken thread caused a switch to momentarily (about 20 ms) interrupt a current as the switch arm moved from its weighted position to its unweighted position, and the momentary interruption would be recorded on a paper chart.

His first design was an open rectangular frame of square aluminum tubing with a screen of fine copper wire at both ends.

The modern chronograph consists of two sensing areas framed by rods topped by diffusing screens or artificial lighting above (or below) along with optical sensors that detect the passage of the bullet.

The time it takes the bullet to travel the distance between the sensors is measured electronically from which velocity is calculated and displayed.

Advanced ballistic chronographs include a type employing Doppler radar to measure bullets in free flight at various distances; another is a device mounted at the end of a barrel, which uses magnetic field sensors for the measurement of a bullet's velocity as it exits the muzzle.