Rolex 4030

History: Rolex decided not to simply shoehorn the Zenith El Primero into a Rolex case. Instead, they modified it. By the time they had finished, the El Primero had been through around 200 modifications and more than half of its original components had been swapped for those judged more suitable. It also had a new name; the Cal. 4030.

Of the myriad changes, the most significant was the drop in frequency. The Zenith movement arrived at Rolex’s door with a beat of 36,000vph and left at a more stately 28,800vph, matching the rest of the brand’s lineup. It’s the balance speed that gives the trademark sweep to the seconds hand, while also ensuring the caliber’s components receive less wear and tear and a longer time between services. (It was in direct contrast to the Valjoux movement, which Rolex had raised from 18,000vph to 21,600vph).

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