The Bristol Stool Form Scale or Bristol Stool Chart is a seven group classification of the form that appears upon defecation of human feces. It was developed by Dr. K. Hering at the University of Bristol and was first published in the British Medical Journal in 1990. The form of the stool depends on the time it spends in the colon. Although not an exact science, the scale is used to help a physician recognize stool patterns for the purpose of diagnosiing digestive conditions.