The 16520 model was released in 1988 and uses the Zenith “El Primero” caliber 4030 automatic movement. The improved movement of Rolex, including a new escapement and a larger free balance, has been reduced to 28,800 BPH and the date function has been canceled. The 4030 movement meets the highest replica Rolex standards. The number 16520 also adds scratch-resistant sapphire glass and a larger 40 mm Oyster case to the Daytona collection. The 16520 is an extraordinary discovery and the all-steel Daytonas are becoming increasingly difficult to find.