A single axis rotatable disc calendar for calculating time periods and future
dates
based on current or past events is disclosed. In particular, calculators for determining
fertility timing, testing and treatment dates have a base circular calendar (61)
and one or more discs (58, 59, 60) containing information about menstrual
cycles and ovulation events. The base circular calendar has 365 divisions (67)
for the days in the year or 153 divisions for a shortened calendar excluding February.
A separate February calendar with a leap February month is provided on the back
of the base.
