Munsell (1858-1918) added three dimensions to the color wheel to differentiate hue, saturation and value. His system used a vertical axis which runs from white to black in 10 steps to represent lightness (or value). At the middle value level was hue circle defined by five equally spaced hue dimensions. Finally, each hue was calibrated in equal chroma steps from zero (pure gray) to the maximum color intensity of the paints or inks used for each hue. A coordinate numbering system allowed each color to be named according to its position on the chart.