The Bristol Stool Scale or Bristol Stool Chart is a medical aid designed to classify the fæces form into seven groups. It was developed by Heaton and Lewis at the University of Bristol and was first published in the Scandinavian Journal of Gastroenterology in 1997. Lewis drew inspiration from the eye charts found in eye examination offices. The form of the stool depends on the time it spends in the colon. The seven types of stool are: