Divers or ISO 6425
If your watch has "ISO 6425" or "Divers" and a depth number written on the dial or case, you have a watch designed for diving and certified up to a standard, unlike watches without them. The ISO standard means the watch is guaranteed by the manufacturer to handle depths of at least 100 meters as well as an extra 25 percent of that depth if the water is completely still. Additionally, watches that measure up to this standard have significant shock, magnetic, and saltwater tolerance, and provide an indication that it's running in total darkness. If you're going to dive deep, go with one of these watches.