In the second half of the 1940s following the launch of the definitive "Oyster" case shape Rolex introduced a variety of different watches with a diversity of movements for this case. It was predominantly used for the perpetual model with date window later named DateJust until the 1950s when a second aperture was added introducing the weekday at 12 oclock the celebrated Day-Date. The "Oyster" case was also produced with different chronograph movements either with a constant seconds register or three subsidiary dials including the hour register. The most complicated chronograph version cased in the "Oyster" style is the famous "Dato-Compax" later nick-named "Killy" by collectors featuring a full calendar on top of the chronograph mechanism.