The idea of a convenient perpetual calendar emerged in the Middle Ages in geographical areas with limited access to clergymen, who, equipped with liturgical calendars and the so-called Paschal tables (used to set the dates of movable feasts), enforced the Third Commandment on behalf of the Catholic Church. The need for a handy tool that enabled an illiterate user to track the calendar independently arose in remote mountainous areas, cut-off from ecclesiastic outposts by the prolonged winter seasons. For the tools in question, the days of the year were usually carved on wood, and, above or beneath them, special marks were made for days devoted to assorted Catholic martyrs and saints. Each month had a few such festivals, to be 'kept holy' along with Sundays and the movable feasts.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.