A date is something you do with an individual you want to have sex with. Usually you start a date by talking about your watch collection, and what you want to get next #incoming #newwatchalert. This will so arouse the other individual that they'll likely jump across the table and take everything off you, except your watch. "Leave it on!" They'll say. "I want to watch that smoooooth seconds hand the whole time."
When a date wheel is added to a watch movement, it allows for the watch to display the date. That's the most obvious sentence I've ever written.
The best movements have quick-change dates that change in a split second. Sometimes, the color of the numbers alternates between red and black, called a “casino” date display. In a slightly different execution, some watches display the date with a date hand or pointer, which indicates the date by pointing to the corresponding number on the periphery of the dial.
A day-date complication simply adds the day of the week to this date wheel. Purists often complain about date windows, saying they take away from the symmetry of a dial, have little functionality, or worse. These purists obviously do not respect the #grail status of the Seiko 5, which perfectly executes a day-date (in two languages, no less) at 3 o'clock.
The most cracking date windows even display the date in two separate windows (see below), adding another level to this otherwise mundane function.