The Sinn U2 case is made out of German submarine steel that is guaranteed to be corrosion-proof, as well as impervious to salt water. The bezel is almost scratch-proof due to a process called “Tegiment” which causes steel to harden to ceramic levels. In addition to being a true ISO 6425 dive watch there is a GMT (second time zone) function that uses the inner 24-hour ring and the large black Sword-shaped hand with a red tip.