Inscribed: "C’est la Planche 3 divisée en 72 parties égales avec cette condition que les zônes représentant le rouge, le jaune et le bleu, partagent en deux moities les trois parties où elles se trouvent."

This plate superimposes a radial grid with 72 equally sized divisions over the "circular zone of continuous colors" illustrated in Plate III. The area between the two letters "R" on the inner and outer circles indicates the color red in its purest hue and also marks the middle point of a larger zone of hues in which red can be found. Similarly, the area between the two letters "J" indicates pure yellow and marks the middle point of the zone of hues in which yellow can be found; the same applies for the pure blue between the two letters "B."