 Rolex introduced the Day-Date model in 1955, which was the first wrist watch to feature both a day-of-the-week aperture window and a date aperture window.The Day-Date was somewhat similar to the Rolex Datejust at 36mm in diameter, but featured a slightly thicker case.The Rolex Milgauss was introduced in 1956 with a Reference Number of 6541.