The shadow cast by a pointer or Gnomon in sun light has been
used to indicate the time for thousands of years. The movement
of this shadow is not constant throughout the year and the time
so determined can be over 14 minutes ahead or behind the time
kept by the best mechanical clocks. This is due to the variation
of the speed of the Earth in its orbit about the Sun and the
inclination of the Earth's axis to the plane of this orbit. The
difference between these two times is known as the equation of
time. Another complication is caused by Time Zones. When the Sun
passes directly to the South of you, it is noon according to the
Sun. For someone a few miles to the East of you, however, the
Sun has already passed through this due South condition. For
someone to the West of you, it still has to reach Solar noon.
Thus in a given Time Zone, in which all mechanical clocks are
supposed to be synchronized, Sundials will read different times
depending on their longitude. This time difference is usually
added to the "equa