The Rolex Submariner 16618LB is powered by a perpetual, mechanical, self-winding caliber 3135 jewel movement. The ease and convenience of a perpetual movement is unparalleled, as any type of movement, including daily wear, will keep the watch in motion. The movement is also certified by the independent non-profit group the Swiss Official Chronometer Testing Institute (COSC). The COSC puts the movement through a rigorous 15 day test, exposing it to various elements and conditions to ensure precision and the highest level of timepiece craftsmanship. Its seal of approval is engraved on each of Rolex’s Perpetual movement timepieces.