An altitude sundial in which the time is shown by light rays passing through a small hole in a ring, giving a spot of light on a set of hour lines on the inner surface of the ring. Such dials are sometimes called 'poke' dials: 'He drew a dial from his poke. . . And says, very wisely, "It is ten o'clock"' (As You Like It). Since the sun's altitude at a given hour depends on the date, being greater in summer than in winter, a fixed pinhole with a set of hour lines parallel to the axis of the ring would be correct only for one date each half-year. There are two ways of providing for the whole range of dates. The first is to make the hour lines slope and to divide them into three parallel rings, one for winter, one for summer, and one for spring and autumn. The second is to make the pinhole in a small piece of a ring sliding within the main ring adjustable according to the season. This gives an approximately correct set of readings on hour lines parallel to the axis, though with some seasonal errors.