Currently the most widespread type of watch glass. It's very hard and has a high conte Watches marked with water tightness 100M/10ATM are designed for swimming and snorkeling and free diving without breathing apparatus. 100M/10ATM indicates the degree of water resistance standardized by ISO 6425. ISO tests include temperature changes, depth, pressure (water and air) for different times under the rest and during manipulation with the operative part of the watch.nt of silicon thanks to which it's highly scratch- and impact-resistant.