Regular haircut
Human scalp hair grows on average about one eighth inch per week or one half inch per month. Most clipper guards are numbered in eighths of an inch. The number of the guard denotes the number of weeks of hair growth left on the scalp when a clipper with a certain numbered guard is guided over the head with the guard in contact with the scalp. A #1 guard leaves 1/8 inch (3 mm), one week's growth of hair, on the scalp; a #2 guard leaves 2/8" (6.3 mm), two weeks' hair growth, on the scalp; a #3 guard leaves 3/8" (9 mm), three weeks' hair growth on the scalp; and so on.
Hair theft
Hair theft has been a recurrent problem in various parts of the world where human hair is in demand either for commercial products such as wigs and hairpieces, or for sexual fetishes. As hair has a high commercial value – in the mid-19th century it was regarded as worth twice its weight in silver – opportunist thieves have targeted long-haired women, and less commonly men and children, with the aim of stealing their hair. Hair thieves have typically sought either to surreptitiously cut off hair in public places, or have mugged people and shorn their heads. The crime of hair theft has been widely reported in North America, Europe, Asia and Australasia over the course of at least 300 years.