Shepherd's dial
A shepherd's dial (also known as a pillar dial or cylinder) is a type of sundial that measures the height of the sun via the so-called "umbra versa". Its design needs to incorporate a fixed latitude, but it is small and portable. It is named after Pyrenean shepherds, who would trace such a sundial on their staffs. This type of sundial was very popular in the 16th, 17th and 18th centuries. History. Since the ancient Roman era, people have created sundials which tell the time by measuring differences in the sun's height above the  horizon over the course of the day – Vitruvius describes them as "viatoria pensilia". The earliest description of a shepherd's dial as known today was written by Hermann of Reichenau, an 11th-century Benedictine monk who called it a "cylindrus horarius". It was also known in the Middle Ages as a "chilinder oxoniensis" (Oxford cylinder). Such sundials did not need aligning north-south and so became very popular, appearing in Renaissance artworks such as Holbein's 1528 "Portrait of Nicolaus Kratzer" and his 1533 "The Ambassadors". Variants. A Slovenian shepherd's dial is a flat dial in the shape of  a sector of a circle. It is hung vertically and measures the altitude of the sun. A movable peg adjusts for the changing seasons.