“Allowing for the two types of year (leap and normal), and the seven possible days a year can start on, there are only fourteen calendars to choose from. When I was shopping for a 2019 calendar (non–leap year, starting on a Tuesday), I knew it would be the same as the one for 2013, so I could pick up a secondhand one at a discount price. Actually, for some retro charm, I hunted down one from 1985.”