A clock has a clock face in the form of an axially symmetric solid, e.g. a sphere, a cone or a cylinder. Clock hands extend around the clock face following a helical path, and time-indicating markings are arranged on all the surfaces of the face. It is therefore possible for a complete set of these markings to be seen from any direction relative to the clock face. The hands are normally driven by a conventional clock movement, there being an hour hand and a minute hand. However, it would be possible in some applications to have only a single hand, e.g. a minute hand, and to drive the clock face relative to the hand. The markings are arranged along helical paths, corresponding to the helical shape of the hands.