Chronoscope, England, 1921-1939

"Chronoscope" for measuring reaction times, electrical mechanism in wooden case, lacks actuating switches, by National Institute of Industrial Psychology, London, early 20th century

A chronoscope is used for measuring small amounts of time, to an accuracy of 1/1000th of a second. They became popular with the emergence of laboratories of experimental psychology in the late 19th century, where they were used to try to determine the speed of thought.