So it were the military and sportsmen that used the first chronographs. The soldiers used it to time their excersizes and operations. And because many of these operations were carried out at night, there was the need of an illuminated dial. Numerals and hands were treated with a fluorescent material, Radium. Military chronographs are recognized by the easy to read, black dial and an inscription on the back indicating the army unit.
Military watches are quite similar, because of the regulations and specifications they have to meet.
A military chrono may be fitted with a telemeter scale on the edge of the dial. This can be used to determine the distance of enemy artillery or thunderstorm. When the chrono is started at the perception of the fire and stoppped at the explosion, the central hand will indicate the distance. Chrono's used by sportsmen are most likely used as stopwatches. The dial indicates the number of seconds, devided in fifths of a second.