Bader
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Time Zone indicator
It is for pilots crossing international times zones.
Top section is 6am to 6pm
Bottom section is 6pm to 6am
Image shows the time as approaching noon.
Hope this helps 
Questions on the XXI 3815 and 3817 for those that actually have them.
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 hav...
Breguet 3817 - subdial at 3 o'clock tells you, wether it is night or day.
Hi there, I have a 3817 and the subdial at 3 o'clock is fix-linked with the standard hour hand and shows you night/day. Best, Heiko
Time Zone indicator
It is for pilots crossing international times zones. Top section is 6am to 6pm Bottom section is 6pm to 6am Image shows the time as approaching noon. Hope this helps ...
Now I understand
Thanks Heiko and Steve So it looks like the 3810 and 3817 both have the 12 hour register at the 6 o'clock position and the 3815 can only count up to 60 minutes as a chrono. I guess you could count the hours on the 3815 using the bezel. Steve