Device for the exact calculation of the fertile days of the woman (Machine-translation by Google Translate, not legally binding)

摘要

A device for the exact calculation of the fertile days of the woman, characterized by the fact of being constituted by three regulated and graduated spheres complemented with each other with relative movement of rotation, of which there is a posterior one of greater diameter; another central one of smaller diameter, and another one of intermediate diameter between that of the two aforementioned spheres; the base sphere being divided essentially into thirty-one spaces numbered correlatively, next to its periphery, of which the last three, corresponding to figures 29, 30 and 31, have their upper edge lowered, and carry along the edge the initials of the months "Febr., Apr., Jun., Sep., and Nov." corresponding to the months of the same nomenclature. (Machine-translation by Google Translate, not legally binding)