When I saw this
free moon calendar, I honestly thought it meant a calendar that you could use to tell what day of the week it was based on the moon. Then I realized I'm an idiot. But think about how cool that would be. To go in a cave or something for a long time and then to walk out one night, look up at the sky during, and go “Oh, it's totally March 19th. Duh.”
But I'd probably just cheat and look at my watch. Because I'm sneaky like that.