Rolex 1555

History: The 1555 is a variant of the 1530 with the added utility necessary to drive the second calendar display. Although the new caliber had the same diameter as the rest of the 1500 series at 28.5mm, it was the thickest out of the entire range, measuring 7.03mm top to bottom. The 18,000 VPH frequency gave the Day-Date a five ticks per second beat, not quite the smooth sweep of later models, but still highly accurate and steadfastly reliable.

Rated as a 25-jewel movement, it actually contained an additional three or four jewels in the calendar mechanism that, while not the handy Quickset version that made its debut in the seventies, benefitted from the instantaneous midnight date change system still used by Rolex today.

In common with its sibling calibers, the 1555 shared the same setup of free-sprung Nivarox hairspring with Breguet overcoil and a balance wheel regulated by Rolex’s patented Microstella screws. Protected by KIF Flector shock absorbers, it used a traditional stone lever escapement and had a power reserve of 42 hours.

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