Rolex watches have their quick-changing date window at 3 o'clock - as seen on the Rolex Submariner, Datejust, Day-Date, Milgauss, and just recently, the Sea-Dweller. This has been a fixture on Rolex watches with a date since 1945.
In 1953, Rolex introduced an enhancement to the date window, called the Cyclops. Named after the one-eyed giant of Greek mythology, the Cyclops lens is placed outside of the watch crystal, on top of the date aperture, in order to magnify the date.
While the bezel of the Rolex Submariner rotates, the Cyclops Lens is stationary on top of the date.