The quartz Rolex was introduced in 1970 as reference 5100. The initial pilot series production was completely sold out prior to delivery. Model 5100 was the first Rolex to have a sapphire crystal and the quick date change mechanism. It was also revolutionary for the new case design, much more angular in its shape than the Oyster case. Designed to be made in very limited quantities only, each Rolex Quartz is engraved with the limited edition number. The present is number 623.