These digital clocks set themselves automatically by tapping into the time signal broadcast from a cesium fountain atomic clock located in Boulder, Colorado. Accurate to 1 second every 60 million years, the atomic clock signal is broadcast all over North America by the National Institute of Standards and Technology.If you need to know the time while in the shower, you’re probably already late! Find out exactly how much–down to the nanosecond–with this incredibly precise waterproof clock. The suction cup on the back easily adheres to tile, glass or porcelain. Includes day of the week and alarm clock. Requires 1 AA battery, not included.