The time is read by the shadow of the gnomon (the antenna piece) on the inner surface of the 1x2 jumper plates arranged in an arc at 15-degree increments. The lines between the plates indicate each hour, and the stud on the underside indicate the half hours.
The photo above was taken at 10:27 Daylight Saving Time on March 22, near 41 N lat. and 95 W long. On this date and in this location, the time shown on sundials is about 27 minutes behind that shown on local clocks. Because of the one-hour shift during daylight saving time, the sundial time is also one hour slower than clock time. Subtracting 1:27 from 10:27 gives 9:00, which is the time indicated by the gnomon shadow in the photo.
As it happens, 1xN plates placed snugly against one another on the underside of a 1x4x5 arch create the 15-degree angle needed. This is the most compact method of making a semi-circle divided into 12 equal segments.