Diver's or ISO 6425
If your watch has "ISO 6425" or "Divers" and then a depth number written on the dial or case, you've got a watch designed for diving and certified up to a standard — unlike watches without ISO markings. This ISO standard means the watch is guaranteed by the manufacturer to handle depths of at least 100 meters (if no number is given) as well as an extra 25 percent of that depth if the water is completely static. Additionally, watches that measure up to this standard have significant shock, magnetic, and salt water tolerance, and provide an indication that it's running in total darkness. If you're going to go deep, go with one of these watches.