World's Most Accurate Sundials
Sundials and plans for sundials calibrated for the specific mounting location. This calibration is necessary to adjust the shadows for the height of the sun (lattitude adjustment), these clocks go further and adjusts for longitude so the clocks will display time-zone time instead of solar time. Standard time or daylight time zone calibration is an option. Even still the sundials will vary because of the "equation of time" due to differences in the speed of the Earth at different places along its orbit of the sun. So these come with a reference table for the adjustments needed, which you have to do after reading the sundial.