What is claimed is the ornamental design for a calendar sheet, as shown and described.
FIG. 1 is a plan view of the calendar sheet;
FIG. 2 is an enlarged section view of the bottom portion of the calendar sheet depicted in FIG. 1; and,
FIG. 3 is a plan view of the calendar sheet for a leap year.
The broken line showing of the year on the calendar is included for the purpose of illustrating environmental structure and forms no part of the claimed design. The rear of the calendar sheet forms no part of the claimed design.