(137) The color score presents four large divisions or color fields made by the intersection of the equator with the meridian of green. Above the centre are all light colors, and below it are all dark colors. To the right of the centre are all warm colors, and to the left are all cool colors. Middle green (5G 5/5) is the centre of balance for these contrasted qualities, recognized by all practical color workers. The chart forms a rectangle whose length equals the equator of the color sphere and its height equals the axis (a proportion of 3.14:1), representing a union and balance of the scales of hue and of value. This provides for two color dimensions; but, to be complete, the chart must provide for the third dimension, chroma. (138) Replacing the chart around the sphere and joining its ends, so that it re-forms the transparent envelope, we may thrust a pin through at any point until it pierces the surface of the sphere. Indeed, the pin can be thrust deeper until it reaches the neutral axis, thus forming a scale of chroma for the color point where it enters (see paragraph 12). In the same way any colors on the sphere, within the sphere, or without it, can have pins thrust into the chart to mark their place, and the length by which each pin projects can be taken as a measure of chroma. If the chart is now unrolled, it retains the pins, which by their place describe the hue and value of a color, while their length describes its chroma. +Pins stuck into the score represent chroma.+ (139) With this idea of the third color dimension incorporated in the score we can discard the pin, and record its length by a numeral. Any dot placed on the score marks a certain degree of hue and value, while a numeral beside it marks the degree of chroma which it carries, uniting with the hue and value of that point to give us a certain color. Glancing over a series of such color points, the eye easily grasps their individual character, and connects them into an intelligible series. (140) Thus a flat chart becomes the projection of the color solid, and any color in that solid is transferred to the surface of the chart, retaining its degrees of hue, value, and chroma. So far the scales have been spoken of as divided into ten steps, but they may be subdivided much finer, if desired, by use of the decimal point. It is a question of convenience whether to make a small score with only the large divisions, or a much larger score with a hundred times as many steps. In the latter case each hue has ten steps, the middle step of green being distinguished as 5G-5/5 to suggest the four steps 1G, 2G, 3G, 4G, which precede it, and 6G, 7G, 8G, and 9G, which follow it toward blue-green. [Illustration: Fig. 23. COLOR SCORE--(or Nº 6 in Plate III)--GIVING AREAS BY H, V AND C.] +The score preserves color records in a convenient shape.+