1. Hunter, R. S. 1948. Photoelectric color-difference meter. J. Optical Soc. Am. 38: 661.
2. Henry, A. Gardner Laboratory Inc., Bethesda, Md. Description and instructions for Hunter color and color-difference meter.
3. Sutton, C. C., Roberta C. Ambler, and D. Arkin. 1952. Color measurement as a quality control tool. Food Technology 6: 190–194.