Rolex 1831 is very unique in that it is the rarest reference of Rolex ever made to carry it its own movement. Only 9 pieces were ever made, all on special order by the 1970s. All were made in Platinum. It is also known as ‘The King of Day-Dates.’ The case measures 36 mm and with its weight of 290 grams, it is thought to be the heaviest Rolex watch ever. The diamonds on the bezel and hour markers are set further towards the outer part of the case than is normally seen with Rolex day dates.