Sundials are wonderful instruments but their accuracy is only as reliable as its set-up. To that end, setting and calibrating your sundial requires careful placement and attention to detail. In the end, your sundial may become a pleasant alternative to the digital read-out on your watch or cell phone.
Check your sundial's manufacturer information. Sundials are only exactly accurate at the latitudes for which they were designed. In other words, a sundial built in Barcelona will not accurately gauge the time in Manchester. You will need to compensate for this later.Set your sundial so that your gnomon (Greek word for indicator) points directly north, using a small compass. Compasses, of course, point to magnetic north, so sticklers for accuracy may want to adjust their sundial accordingly to true north, using a magnetic declination map. You can also site your sundial, at exactly noon, local time, so that it also reads the time as exactly noon.Adjust your sundial's base so that it matches your latitude, as per your manufacturer's information. A sundial built for 37ºN, but used at 51ºN, will have to be wedged up by 14º. Use a protractor to ensure that your gnomon's angle to the horizontal matches your latitude. Alternatively, you can site along the line of the gnomen at night, until it points directly at the North Star.Remember that there is a difference between "sun time" and "clock time." The day is not actually 24 hours long. As a result, and throughout the course of a year, your sundial will be fast or slow by up to 15 minutes.