Perpetual menstrual cycle calendar - two halves of rotary disc are adjustable to suit number of days in a month

摘要

A sheet is folded around a disc to which it is secured by e.g. a rivet (7) to leave the upper edge of the disc visible above the edge of the sheet which indicates the period of fertility and the dates on which male or female babies are more likely to be conceived. The disc periphery has members indicating the date of the month and, so that the disc can be adjusted for different length months, the disc is formed from two similar halves with concentric holes (9), (10) for the rivet (7). A rivet (15) or (16) passes through a hole (19) or (20) and a slot (17) or (18) on each half so that the halves can relatively rotate about the rivit (7) to cover or conceal the dates 29, 30 and 31.