A watch - one with a dial - is a very visual thing. From them you can not only determine the time, but also observe its flow, watch how the hour passes or, if there is a second hand, how the minute runs. Calendars do not provide this option. Only show the "general plan" of the year, month; at best one day if the calendar is tear-off. How do you show the course of the day on the calendar?
Very simple - decided Oscar Diaz, the same person who created the RGB vase. His "self-printing" calendar, which so far exists only in the form of a prototype, is a jar of ink that gradually permeates the relief image of the numbers of the month, while the time of coloring of one number is just a day.
By the way, this is necessary not only to push philosophical topics. One glance at such a calendar is enough to determine today's date, there is no need to tear off the pages of the calendar or move the "window" every day. But I must admit that electronic watches with a date stamp do the same well. And this design is quite cumbersome, and the ink can be dropped inadvertently, and if the painted numbers get dirty, it’s just a guard.
But the concept is still interesting. A variation on the theme: an ink sprout slowly gaining strength.