Today you may carry a smart phone to help you calculate astrological charts while traveling. “For medieval physicians, the mnemic apparatus of choice was what is sometimes today known as a folding almanac or a belt book. There are thought to be just 29 such almanacs that have survived to the present day.”
The almanac was made using vellum, a tough paper made from an animal skin. It was folded, strung on a cord and hung from the belt. It was particularly useful for doctors as they made house calls. Read More from The Atlantic.