Having a formula to calculate time as per Sun Position should show some minor difference of time within cities at a difference of few 100 miles.
closed as not a real question by Manishearth♦ Dec 26 '12 at 13:03
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You are talking of sundials.
Latitute and seasonal changes are taken care of in the design of the hour-lines.
Yes, the sundial is calibrated to measure the the astral time, not the time given by the agreement of countries as a convention, the time zones., which are swaths of 1 hour.