iwc Schaffhausen Mode D'emploi page 21

Moon phase display
18 | 19
1 2 3 4
Full moon Waning moon New moon Waxing moon
The moon phase display is set automatically by the date-mechanism and is
thus always correct. The reduction ratio is so precise that the display will
only deviate by a single day after 577 years.
Setting the perpetual calendar
Pull the crown to position 1. In this position, you can advance the perpetual
calendar in steps using the quick setting function by rotating the crown slowly
to the left. Adjustment of the perpetual calendar must not be performed
between 20.00 and 2.00.
Please note: You must not advance the perpetual calendar beyond the
valid date. The complicated movement is permanently mechanically pro-
grammed and cannot be turned back without intervening in the movement.
If, however, you have adjusted the perpetual calendar beyond the valid
date, you have two possible courses of action:
Either you must stop the movement by pulling out the crown to position 2
until the perpetual calendar setting once more corresponds to the valid
date. This is appropriate in the event of a small forward misadjustment by
only a few days. Or, you must take your watch to your watchmaker, who
will be able to adjust the movement to reset the perpetual calendar. This is
required in the event of larger misadjustments.