The Day-Date was originally designed to be a precious instrument for everyday use. Thanks to a watchmaking prowess that was unprecedented at the time, it offered a solution to those requiring complete mastery of their personal calendar: the Day-Date was the first self-winding, waterproof chronometer wristwatch to display the date and the day of the week spelt out in full in two separate windows. Both change simultaneously at midnight. This revolutionary switch continues to fascinate, nearly seven decades later.