Read a guide to the common ATM ratings for watches. 1 ATM - Splashes, Rain, etc 3 ATM - Showering, Washing Up, etc 5 ATM - Swimming, Bathing, etc 10/20 ATM - Snorkeling, Wind Surfing, Diving, etc Brought to you by Breo watches. Visit the Breo website to view their range of waterproof watches - http://www.breo.com