Perpetual almanac. 17th-century illustration of a perpetual almanac (a type of calendar) devised for the English county of Staffordshire, and presented in the form of a clog almanac, which consisted of a log of wood with four edges, shown here as four vertical blocks. Each notch represents a day, with large notches representing a week. Each of the edges shows a period of three months, with the whole representing a year. The symbols represent religious festivals and phases of the moon. The dedication by English naturalist Robert Plot (1640-1696), first Professor of Chemistry at the University of Oxford, and the first keeper of the Ashmolean Museum, is to English antiquary Elias Ashmole (1617-1692). Artwork from Plot's 'The Natural History of Staffordshire' (1686).