The third side may be drawn in any shape desired. Cut out the triangle to use as the sundial's gnomon. Tape the gnomon to the noon line of the sundial. When completed, the gnomon should be vertical to the face of the sundial. Position the sundial so the gnomon is pointing directly North and read the time from the shadow cast by the gnomon on the sundial.
Extensions Have the students compare the time from the sundial to the time from a clock.
The two will probably not read the same. Three corrections that can be made may be discussed with the students. Daylight saving time. If the sundial is read during daylight saving time, one hour must be added to the reading. Your position compared to the time zone meridian of your time zone.