Vacheron Constantin Overseas Gen 1 Automatic Large model, 42042/423A-8724, with Blue sunray dial and Cal.1311 based on GP3100.
The movements are frequently discussed about Gen1, but according to the legend, 42040 and 42050 have Cal.1310, 42042 and 42052 have Cal.1311.
So what is the difference between 1310 and 1311?
In fact, I haven't come to the exact information about it.
Probably, the product with some improvement to 1310 is 1311.
GP3100 released in 1994 by Girard Perregaux. Soon after release, there were three issues. From there, imagine the difference between 1310 and 1311.
1. Minute hand delay. The delay from when the minute hand is set to when the gear meshes and the minute hand moves.
2. Minute hand jump. The phenomenon that the minute hand moves back and forth when the crown is pushed in with the minute hand set.
3. Feel when adjusting the minute hand. If this feel is too light or too heavy, it directly affects usability. I heard the early GP3100 felt too light.
Last but not least, my 1311 solves these three issues.