Time in the Unite 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 for part of the year. The time zone boundaries and DST observance are under the authority of the Department of Transportation. Official and highly precise time keeping services (clocks) are provided by two federal time agencies: a Department of Commerce agency, the National Institute of Standards and Technology (NIST), and its military counterpart, the United States Naval Observatory (USNO). The clocks run by these services are kept highly synchronized with each other as well as with those of international time keeping organizations.