this clock be excellent for a bare bone digital clock . when I first plug it in , the time be less than one second off atomic time . I have plug and unplug the clock many time the past 6 month and the time be now about 26 seconds faster than actual time . the time and calendar can be manually adjust -- read the manual . the Daylight Saving Time can be disabled for portion of the U.S. which do not observe DST . the DST setting can be set to the new DST rule or old DST rule in the unlikely event Congress decide to go back to the old rule . by default , the clock be set to the new DST rule . in case of power failure , the display will turn off , but the clock will still run and the alarm will sound if the alarm be activate . the clock use 4 lr44 battery as backup . the manual say the battery last 3 year before need replacement . when change the battery , leave the clock plug in . this way , you will not need to manually reset the time and calendar . the downside to this clock be the blinking colon '' : '' and the display be bright . there be no dimmer switch .