Eberhard & Co Watch Chrono 4 21-42 Rubber 31073.05 CN. Chrono 4 21-42 celebrates 20 years of Chrono 4. After having entirely transformed the reading of time at the dawn of the new millennium, this iconic model is the first and only chronograph in the history of watchmaking to boast 4 aligned counters. The Chrono 4 21-42‚ name is inspired by the lucky numbers recalling the year of the launch and the size of the case.