What factors influence the time read by my sundial?
There are 4 main factors:

Latitude
Shepherds Watch sundials are calibrated for 40 degrees N. If you are north of 40, the dial will read a bit earlier than clock time. If you are south of 40 the dial will read a bit later than clock time.

Longitude
Time Zone meridians are every 15 degrees, e.g., Eastern is 75°, Central is 90°, etc. Clocks keep the same time throughout the Time Zone. For every 1 degree east of the Time Zone meridian, subtract 4 minutes from the dial to get clock time. For every 1 degree west of the Time Zone meridian, add 4 minutes to the dial to get clock time.

Equation of Time
Our clocks assume that the day is exactly 24 hours long every day of the year. But the solar day, i.e. the time it takes the Sun to return to the meridian from one noon to the next, is not exactly 24 hours. It is several seconds more or less. This is due to the shape of the Earth's orbit and the angle the Earth is tilted to the plane of the orbit. Sundials mark solar days and tell solar time. The difference between solar time and clock time is called the "Equation of Time." The Equation of Time can be as much as 16 minutes.

Daylight Saving Time (DST)
DST is the social convention of setting the clock an hour ahead of standard time between April and October in order to provide more sunny hours in the evening is called Daylight Saving Time. When Daylight Saving Time is in effect, add an hour to the sundial reading.

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