In each of our models, we calculate both hue and what this article will call chroma, after Joblove and Greenberg (1978), in the same way—that is, the hue of a color has the same numerical values in all of these models, as does its chroma. If we take our tilted RGB cube, and project it onto the "chromaticity plane" perpendicular to the neutral axis, our projection takes the shape of a hexagon, with red, yellow, green, cyan, blue, and magenta at its corners (). Hue is roughly the angle of the vector to a point in the projection, with red at 0°, while chroma is roughly the distance of the point from the origin. More precisely, both hue and chroma in this model are defined with respect to the hexagonal shape of the projection. The chroma is the proportion of the distance from the origin to the edge of the hexagon. In the lower part of the adjacent diagram, this is the ratio of lengths , or alternatively the ratio of the radii of the two hexagons. This ratio is the difference between the largest and smallest values among R, G, or B in a color. To make our definitions easier to write, we'll define these maximum, minimum, and chroma component values as M, m, and C, respectively. To understand why chroma can be written as , notice that any neutral color, with , projects onto the origin and so has 0 chroma. Thus if we add or subtract the same amount from all three of R, G, and B, we move vertically within our tilted cube, and do not change the projection. Therefore, any two colors of and project on the same point, and have the same chroma. The chroma of a color with one of its components equal to zero is simply the maximum of the other two components. This chroma is M in the particular case of a color with a zero component, and in general. The hue is the proportion of the distance around the edge of the hexagon which passes through the projected point, originally measured on the range but now typically measured in degrees . For points which project onto the origin in the chromaticity plane (i.e., grays), hue is undefined. Mathematically, this definition of hue is written piecewise: Sometimes, neutral colors (i.e. with ) are assigned a hue of 0° for convenience of