Years ago I had a XX Transatlantique and now looking to buy another type XX/ XXI.
I haven't found a good answer about the sub dial at 3 o'clock. Some of the reviews say it is a hour counter for the chrono and others say it is to tell day/night time. I have used the sun for that.
On the 3815 I can see it being used to track the hours for the chrono because there isn't a sub dial at 6 o'clock like the 3817.
What am I missing?