This Jumbo LCD Radio controlled wall clock will always show the correct time as it is constantly receiving the MSF UK atomic clock radio timing signal   12/24 h time display Hours, minutes and second display Full digits Date, Month & weekday display Indoor Temperature in Centigrade or Fahrenheit Alarm with snooze function Wall mounting or Table standing  SPECIFICATIONS Clock Dimensions : 23 x 16 x 2.5 cm Batteries: 2 x AA (not included) Large Jumbo Big Digit LCD Radio Controlled Digital Wall Clock, with Indoor Temperature and Humidity Display Popular for use at Home or Work, Perfect for Public Buildings, Warehouses, Shops, Restaurants, Factories, Banks, School, Indoor Sports Halls and Offices etc. where consistently accurate time is needed   Automatic time change for Spring & Autumn and automatic time checks, accurate to 1 second in 10 million years, have automatic set up for time and calendar (where applicable), The National Physical Laboratory (NPL) which is the UK's home of measurement and the nation's timekeeping. NPL is responsible for operating the national time system and making accurate time available across the UK. This clock keep accurate time by picking up the NPL's radio signal, called MSF, which is transmitted on 60KHz from Cumbria. This transmission carries a date and time code that the radio controlled products use to set themselves to the correct time. The signal is controlled by atomic clocks at the radio station and are adjusted to keep in step with the national time maintained at NPL laboratory in London. Down Load User Manual  from here