Reference 2021 is an historical milestone in Rolex production, being the very first chronograph model ever made by the brand. It features all technical and design elements of a chronograph from the 20s, such as a hinged case back, a white enamel dial and an olive single button caliber.It was not until the late 30s that Rolex introduced its celebrated and more robust Oyster design on chronographs, thus it is extremely rare to find an early hinged Rolex chronograph with enamel dial in such excellent original condition.