The release lever on the left side of the case was first used by British RAF pilots during the Second World War. During high-altitude flights, at more than 26,000 ft, the extremely low temperature forced pilots to wear big mittens and thus required an instrument with an especially large push-piece that enabled operation with the thumb. The activation of the start/stop functions with the thumb, which reacts faster than the other fingers, guarantees the most direct response. In the days when sports times were measured manually, it was the thumb that was used to operate the stopwatch.
Douglas Robert Steuart Bader, CBE, DSO & Bar, DFC & Bar, FRAeS, DL (1910-1982) is Britain's best-known Royal Air Force fighter ace during the Second World War and widely considered to be an inspirational British hero of the era.