Until 1945, dates on a calendar watch weren’t easy to read. The only way to do so was simply to cut the dial into 31 sections and pass a hand over each of them day after day. But after the water-resistant watch, Rolex revolutionized the date: for the first time, it was displayed in a date window at 3 o’clock. The trick: a disc numbered up to 31 under the dial rotates one notch each day at midnight. Since then, everyone has adopted this system which gave this legendary watch its name. From one legend to another, there is only one time on the clock: that of a winning Federer serve.