Rolex 3155

History: The Rolex 3155 was the sixth-generation Day-Date movement from Rolex. Calibre 3155 is a self-winding mechanical movement entirely developed and manufactured by Rolex (actually Aegler, but who really cares?) . It features a day and date calendar disc mechanism. Like all Rolex Perpetual movements, the 3155 is a certified Swiss chronometer, a designation reserved for high-precision watches that have successfully passed the Swiss Official Chronometer Testing Institute (COSC) tests. Its architecture, in common with all Oyster watch movements, makes it singularly reliable.

Caliber 3155 stands at 6.00mm tall and features 31 jewels. It was introduced in 1988. It is based on the calibre Rolex 3135, with additional day of week indication. Cal. 3155 is used in the Day-Date Ref. 118000 and remains in production as of 2018. The similar Rolex 3156 was used in the Rolex Day-Date II. The new Rolex Day-Date 40, launched in 2015, uses the next-generation Cal. 3255.

Like most modern Rolex movements, this model has a hacking capability. It is also the first Rolex movement with the double-quickset feature.

Manufacturer: Rolex SA (/ˈroʊlɛks/) is a Swiss luxury watchmaker. The company and its subsidiary Montres Tudor SA design, manufacture, distribute and service wristwatches sold under the Rolex and Tudor brands. Founded by Hans Wilsdorf and Alfred Davis in London, England in 1905 as Wilsdorf and Davis, Rolex moved its base of operations to Geneva, Switzerland in 1919. Forbes ranked Rolex 64th on its 2016 list of the world's most powerful global brands.[Rolex is the largest single high end watch brand. The company is owned by the Hans Wilsdorf Foundation, a private family trust.

Alfred Davis and his brother-in-law Hans Wilsdorf founded Wilsdorf and Davis, the company that would eventually become Rolex SA, in London, England in 1905. Wilsdorf and Davis' main commercial activity at the time involved importing Hermann Aegler's Swiss movements to England and placing them in high-quality watch cases made by Dennison and others. These early wristwatches were sold to jewellers, who then put their own names on the dial. The earliest watches from Wilsdorf and Davis were usually hallmarked "W&D" inside the caseback.

From Wikipedia