1. I.S.O. Recommendation R 5, Diffuse Trans mission Density (Photography);International Organization for Standardization,1955
2. This standard is identical with American Standards Association: American Standard for Diffuse Transmission Density Z 38.2.5,1946
3. American Standard Temperature for Photographic Processing Solution, pH 4.5,1953
4. American Standard Method for the Sensitometry of Medical X-ray Films, pH 2.9,1956
5. Introduction to Statistical Analysis;Dixon,1957