This graph shows us the average year of menarche, a female's first menstrual cycle (often considered the beginning of puberty), from 1860 to 1980 reported by adult female patients at maternity clinics in Norway. It also includes data from Oslo school girls that follow the same trend downward in age. The downward curve flattens around 1960 between the ages of 13 and 14. A graph like this helps to counter a single interpretation of causes for the rise in age of consent laws.