indicates a time 15 minutes from noon, the user likely won't have a way of distinguishing 11:45 from 12:15. Additionally, altitude dials are less accurate near noon, because the sun's altitude isn't changing rapidly then. Many of these dials are portable and simple to use. As is often the case with other sundials, many altitude dials are designed for only one latitude. But the capuchin dial (described below) has a version that's adjustable for latitude. The book on sundials by Mayall & Mayall describes the Universal Capuchin sundial. Human shadows The length of a human shadow (or of any vertical object) can be used to measure the sun's elevation and, thence, the time. The Venerable Bede gave a table for estimating the time from the length of one's shadow in feet, on the assumption that a monk's height is six times the length of his foot. Such shadow lengths will vary with the geographical latitude and with the time of year. For example, the shadow length at noon is short in summer months, and long in winter months. Chaucer evokes this method a few times in his Canterbury Tales, as in his Parson's Tale. An equivalent type of sundial using a vertical rod of fixed length is known as a backstaff dial. Shepherd's dial – timesticks A shepherd's dial – also known as a shepherd's column dial, pillar dial, cylinder dial or chilindre – is a portable cylindrical sundial with a knife-like gnomon that juts out perpendicularly. It is normally dangled from a rope or string so the cylinder is vertical. The gnomon can be twisted to be above a month or day indication on the face of the cylinder. This corrects the sundial for the equation of time. The entire sundial is then twisted on its string so that the gnomon aims toward the Sun, while the cylinder remains vertical. The tip of the shadow indicates the time on the cylinder. The hour curves inscribed on the cylinder permit one to read the time. Shepherd's dials are sometimes hollow, so that the gnomon can fold within when not in use. The shepherd's dial is evoked in Shakespeare's Henry VI, Part 3 (Act 2, Scene 5, Lines 21-29), among other works of literature. The cylindrical shepherd's dial can be unrolled into a flat plate. In one simple version, the front and back of the plate each have three columns, corresponding