The Bristol Stool Chart (BSC) is a visual aid to assist patients and healthcare practitioners identify constipation. There are 7 types of stool shown, with types 1 & 2 indicating constipation, 3 & 4 being the ideal stools (especially the latter) and 5, 6 & 7 tending towards diarrhoea. The harder stools of types 1 & 2 have been evidenced as having a longer whole-gut transit time (WGTT) while softer stools, those similar to 5, 6 & 7 have a shorter WGTT.
Reference: Lewis S, Heaton K. Stool Form Scale as a Useful Guide to Intestinal Transit Time. Scandinavian Journal of Gastroenterology. 1997;32(9):920-924.