Long before sustainability became a trending topic, people invented reusable, perpetual calendars, but the non-digital versions of these are sometimes complicated tables that are hard to interpret.

Just when you think you’ve seen them all, someone comes up with something new and unusual, like the concentric rings of this automated perpetual calendar. What we really like about the design ...

Calendar systems include solar and lunar calendars that guide planting and harvest as well as synchronized electronic appointment books that keep modern societies humming along. Perpetual calendars ...

In the early 1990s, Patek Philippe had long been known for its elegant time-only Calatrava models, and, at the opposite end of the horological spectrum, its perpetual calendars, perhaps the ...