Hi, I was wondering, who determines the exact time to the second, and
how do they know it is unmistakably accurate? Everyone?s watch is
different to the second so they are all just approximate.

Thanks!

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Clarification of Question by csreech-ga on 05 Oct 2004 15:08 PDT

Thanks, that helps a lot!

In the United States, the official time is determined by the National
Institute of Standards and Technology, an agency of the U.S. Commerce
Department's Technology Administration.  The time is calculated by
counting the oscillations of cesium atoms at an atomic oscillator in
Boulder, CO and is kept close to Coordinated Universal Time (UTC), the
international time standard.

The frequency or rate of UTC is computed by the International Bureau
of Weights and Measures (BIPM) located near Paris, France. The BIPM
uses a weighted average from about 250 atomic clocks located in about
50 national laboratories to construct a time scale called
International Atomic Time (TAI). Once TAI is corrected for leap
seconds, it becomes UTC, or the official world time scale. NIST
distributes a real time version of UTC called UTC(NIST) to the public
through its time and frequency services.

A wealth of information can be found on this topic at the NIST
website.  Here is a good starting point that should answer some of
your questions (the source of the above information):
http://www.boulder.nist.gov/timefreq/general/precision.htm

The United States Naval Observatory also has a Time Service Department
which is  the official source of time for the Department of Defense
(DoD) and the Global Positioning System (GPS).
http://tycho.usno.navy.mil/

Is this what you were wanting to know?

www.time.gov is what I use to check (US).

www.time.gov

The purpose of time.gov is merely online access to the current time. 
It is much like calling the telephone time-of-day service at
(303)499-7111 (not a toll-free number).

Plus or minus one second is easy, and close enough for many
applications, but not for GPS or guided miscles. whyisit so gave a
good answer.  Neil