<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2013) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2013) (Learn how and when to remove this template message) </Td> </Tr> <P> Time in the United States, by law, is divided into nine standard time zones covering the states and its possessions, with most of the United States observing daylight saving time (DST) for approximately the spring, summer, and fall months . The time zone boundaries and DST observance are regulated by the Department of Transportation . Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) (an agency of the Department of Commerce); and its military counterpart, the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations . </P> <P> It is the combination of the time zone and daylight saving rules, along with the timekeeping services, which determines the legal civil time for any U.S. location at any moment . </P>

How many time zones does the united states have