Today is the day to set your sundial. On this date the "equation of time" is zero. That means solar time and clock time are in agreement, and noon on your sundial should agree with noon on your watch. This is also true on Sept. 1, Dec. 25 and April 15. The rest of the year, your sundial might run as much as 16 minutes fast or 14 minutes slow. Blame Earth's tilt and elliptical orbit.