The physical chart consists of layers of 8×10 inch photographic film. The chart contains 20 large patches with densities ranging from base + 0.15 to base + 4.90 (OD = Optical Density) in steps of 0.25 OD, equivalent to 95 dB. (If the lightest and darkest small patches are included, the total density range is 5.1 OD = 102 dB.) Inside each large square there are four color squares: light and dark gray, red and blue. The gray patches are 0.15 OD above and below the surrounding square. The difference, 0.30 OD, is a 2:1 contrast ratio.
For more details see Analysis of the Contrast Resolution chart