iwc INGENIEUR PERPETUAL CALENDAR DIGITAL DATE-MONTH Operating Instructions Manual page 11

Setting when crossing time zones:
– When crossing time zones in an easterly direction, you
should simply set the time forwards to the new local time.
– When crossing time zones in a westerly 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
calendar'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 10 p.m.
You must not turn the hands back between 10 p.m. and
2 a.m. This is because the calendar does not move back­
wards by 1 day when the hands are turned back beyond
midnight, but remains on the same day. If you go past the
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end of the calendar's switching phase (i.e. beyond 2 a.m.)
when turning the hands back, you run the risk of the calendar
advancing by 1 day for a second time and thus indicating
1 day too many.
Setting when crossing the International Date Line:
– When crossing the International Date Line in a westerly
direction (you enter the next day, regardless of the time of
day), simply turn the time forwards to the new local time,
and the date change will take place automatically.
– When crossing the International Date Line in an easterly
direction (you enter the previous day, regardless of the time
of day), you must likewise set your watch forwards to the
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