My grandmother had a small desk paper weight sliding calendar from the 60s that she got as a promotional item from a bank. One side had the calendar and the slider and of course the bank name. The other side had a cheat sheet for year/month and what to set things to if you got lost. Think there were some plastic bits to clip over the days that were not in the month but those were lost to time. Think Matt Parker had a vid a few years ago on reusing calendars from previous years. 14 combinations I think was the total number of calendars you had to keep. But I could be remembering wrong.