While there is significant variation in anatomical proportions between people, certain body proportions have become canonical in figurative art. The study of body proportions, as part of the study of artistic anatomy, explores the relation of the elements of the human body to each other and to the whole. These ratios are used in depictions of the human figure and may become part of an artistic canon of body proportion within a culture. Academic art of the nineteenth century demanded close adherence to these reference metrics and some artists in the early twentieth century rejected those constraints and consciously mutated them. Basics of human proportions It is usually important in figure drawing to draw the human figure in proportion. Though there are subtle differences between individuals, human proportions fit within a fairly standard range though artists have historically tried to create idealised standards that have varied considerably over time, according to era and region. In modern figure drawing, the basic unit of measurement is the 'head', which is the distance from the top of the head to the chin. This unit of measurement is credited to the Greek sculptor Polykleitos (fifth century BCE) and has long been used by artists to establish the proportions of the human figure. Ancient Egyptian art used a canon of proportion based on the "fist", measured across the knuckles, with 18 fists from the ground to the hairline on the forehead. This canon was already established by the Narmer Palette from about the 31st century BC, and remained in use until at least the conquest by Alexander the Great some 3,000 years later. One version of the proportions used in modern figure drawing is: An average person is generally 7-and-a-half heads tall (including the head). An ideal figure, used when aiming for an impression of nobility or grace, is drawn at 8 heads tall. A heroic figure, used in the depiction of gods and superheroes, is eight-and-a-half heads tall. Most of the additional length comes from a bigger chest and longer legs. Measurements There are a number of important distances between reference points that an artist may measure and will observe: These are the distance from floor to the patella; from the patella to the front iliac crest; the distance across the stomach between the iliac crests; the distances (which may differ according to pose) from the iliac crests to the suprasternal notch between the