The solution is the idea of Gaston Breitling, who applied it to a wristwatch in 1915.
Until 1915 chronograph were operated by a button in the crown, which started, stoped and reset the stopwatch.
Gaston, son of the founder of the Breitling manufactory, developed a stopwatch mechanism that was more comfortable to use.
An independent button, separated and placed on the side of case, operated the start, stop and reset functions.
Application: Damian Szojda
Other records: Timeline of Watchmaking Innovations