Often used as garden decorations, sundials are ancient time keeping devices that can be calibrated to keep relatively accurate time. Sundials have a triangular blade called a gnomon that casts a shadow on the metered portion of the clock's face, utilizing the Sun's position and motion to measure time. Though the construct of the sundial is relatively simple, there are a few considerations and measures that must be taken to ensure time accuracy.
Find out your latitudinal location. Sundials are made specific to latitude so you must buy one built accurate to your location. The easiest way to find your latitude is by entering your address in an online finder such as itouchmap.com.
Adjust your sundial's position outside, using an accurate timepiece, so that when it is exactly noon, the shadow cast by the gnomon indicates noon as well.
At various times throughout the day, verify that the time indicated is accurate. If it isn't, this means your gnomon is the wrong size for your latitude. You can compensate by elevating or lowering the bottom edge of your sundial until the time reads accurately for all positions on the clock.