Rolex Sea-Dweller 40mm ceramic ref. 126600 is the quintessential deep saturation dive watch. In addition to featuring a waterproof screw-down crown to hermetically seal the case, reference 116600 also utilizes the industry's innovative Helium Escape Valve. This feature releases the gases that collect within the case, thus keeping the crystal intact during decompression stops and protecting the movement. The Sea-Dweller itself boasts water resistance up to 4,000 feet.