The U.S. Naval Observatory and the National Institute of Standards and Technology cooperate to determine a standard world time called Coordinated Universal Time, which can be viewed on time.gov. Other websites such as time.is and timeanddate.com keep accurate online clocks synchronized to this time.
The National Institute of Standards and Technology and the U.S. Naval Observatory compare data measured from atomic clocks to compute a standardized world time; these measurements are accurate to at least 1/10,000,000 of a second. Time.gov displays this time, correcting for the time lag incurred by displaying this information across the Internet. Many other websites offer this information for free; some of the most popular are time.is, timeanddate.com and worldtimeserver.com.