 It is therefore a perennial calendar, with every date fixed to the same weekday every year.Though it was never officially adopted in any country, entrepreneur George Eastman adopted it for use in his Eastman Kodak Company, where it was used from 1928 to 1989.It is sometimes also called "the" 13-month calendar or "the" equal-month calendar, but there are multiple alternative calendar designs that these descriptive labels apply to as well.