SATO M-8400RVe Operator And Technical Reference Manual page 148

Section 5: Programming Reference
Page 5-82
5. Calendar Increment Example:
1998 January 15 (ww=03) plus 48 weeks = week 51
6. The Week Calendar specification follows ISO8601. Days of the
week are numbered 1 thru 7, beginning with Monday. The first
week of the year is the week containing the first Thursday. If
January 1st falls on Friday, it belongs to the last week of the
previous year. If December 31st falls on a Wednesday, it belongs
to the first week of the following year. If Calendar Increment
calculation extends over the year, the result belongs to the week
number of the following year.
PN 9001075A SATO M8400RVe