The ornamental design for a calendar, as shown and described.
FIG. 1 is a front view of my calendar;
FIG. 2 is a rear view of my calendar;
FIG. 3 is a side view of my calendar included to show curvature of the sheet from FIGS. 6 and 7 when inserted in the base as shown;
FIG. 4 is a top view of my calendar included to show curvature of the sheet from FIGS. 6 and 7 when inserted in the base as shown;
FIG. 5 is a bottom view of my calendar;
FIG. 6 is a front detail view of my calendar removed from the base as shown without curvature;
FIG. 7 is back detail view of my calendar removed from the base as shown without curvature; and,
FIG. 8 is a close up detail view of the region 8—8 shown in FIG. 7.
The broken line shapes surrounding the numbers in the calendar are perforations and form part of the claimed designs The remaining broken lines are indicia and form part of the claimed design. The year indicated on the calendar is intended to change from year to year, along with resulting arrangement of days as one of ordinary skill in the art will recognize.