What is a shadowclock?

Answer 1

A sundial = A flat disc with marks around the edge. The marks are numbered. In the middle of the disk is a piece which sticks out at right-angles to the disc. This piece is called the gnomon. The line the shadow of the gnomon makes falls on the edge of the disc and indicates what the time is. Each dial has to be marked specially, depending on the latitude of where it will be used. A sundial from Rome in Italy would not function correctly in Oslo in Norway.