iwc IW3921 Operating Instructions Manual page 24

— 2 4 —
– When crossing time zones in a west­
erly direction, you can set the hands
of your watch back to the actual time
of day. When doing this, however,
you must not move back into the cal­
endar's automatic switching phase,
i.e. beyond 2 a.m. If this situation
occurs when you are travelling west,
you should set the local time of your
destination before 8 p.m. You must
not turn the hands back between 8
p.m. and 2 a.m.
D A V I N C I P E R P E T U A L C A L E N D A R C H R O N O G R A P H