IWC Schaffhausen 5902 Mode D'emploi page 21

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M O O N P H A S E S E T T I N G
Although the watch is limited to a 12­hour display, the movement
makes a distinction between 12 noon and 12 midnight. The moon
phase moves on 1 day at midnight every day (like a date switch). If
your watch has stopped, the moon phase needs to be adapted to
the current moon position. To do this, move the crown into pos­
ition 1 and adjust the moon phase by rotating the crown to the left
or right. You should not use the rapid­advance function between
8 p.m. and 2 a.m. because the movement automatically advances
the moon phase during this period.
Procedure: Consult the daily press or another source to find the
current moon phase (e.g. the Internet, lunar calendar). Count the
number of days from the current date to the next full moon. Move
the moon phase to the "full moon" position and, by rotating the
crown to the left, turn it back by the number of days until the next
full moon.
P O R T U G I E S E R C O N S T A N T - F O R C E T O U R B I L L O N