There are 24 hours in a day and there are 24 Time Zones in the world. Those that live in the United States are familar with Eastern Standard, Central, Mountain and Pacific time zones. When it is 12:00 in Washington, D.C. it is 9:00am in San Francisco, CA. The meridian of a place is the longitude. Standard meridians are every 15 degrees starting in Greenwich England (Longitude=0 degrees) and going around the world. If you happen to live on your standard meridian then the only difference between your sundial and your watch is the equation of time. If you live off your standard meridian then you have to adjust your dial for its longitude. Since one full rotation (360 degrees) of the Earth takes 24 hours we see that 1 hour of time equates to 15 degrees of longitude (360 degrees of longitude/24 hours= 15 degrees of longitude). Therefore each degree of longitude equals 4 minutes of time and each minute of longitude equals 4 seconds.
Example: A sundial at a longitude of 75 degrees (The standard meridan for Eastern Standard Time) reads 12:00, a sundial in Alexandria, VA (Longitude=78 degrees) reads 11:48. Since the difference in longitude between Alexandria and the EST meridian is 3 degrees the time difference is 12 minutes. The EST meridian is East of Alexandria so since the Sun rises in the East it must be earlier as you go West.