Citizen E610 Instruction Manual page 54

(6) Turn the crown to set the day.
 Turning the crown o the right (by one click) causes the day to change in the
order of SUN  MON  ···· FRI  SAT and then back to SUN.
‚ T urning the crown to the left changes the day in the reverse order of
SUN  SAT  ···· TUE  MON and then back to SUN.
(7) Return the crown to the normal position. This completes the correction
procedure.
<Setting to a Non-Existent Date>
The date is automatically changed to the first day of the following month when the
crown is returned to the normal position from the date correction mode. The date
is displayed as shown below if the date should happen to be mistakenly set to a
non-existent date.
Examples: Regular year: February 29, 30 or 31  March 1
Regular year: April 31  May 1
Leap year: February 30 or 31  March 1
Furthermore, since the set day will be displayed for the day, correct the
day as necessary.
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