The Reactor Critical Mass model 75603 dive watch is constructed to provide reliable performance under extreme conditions. Each Reactor watch is individually depth tested and features Reactor's triple O-ring screw down crown and crown protector. The Critical Mass, which also features an extra thick mineral crystal for maximum shatter and scratch resistance, is depth tested to 200 meters. Each Reactor watch, including the Critical Mass, employs a super strong rod and allen head screw system to attach the bracelet to the case. The critical mass has a unidirectional countdown bezel and a superluminova illumination system that will glow brightly for up to 8 hours after exposure to light. Model 75603 has a quartz movement and an ocean blue color dial with day/date display. eWatches.com is an Authorized Reactor Watch Dealer.