This reference was posted on APUG in a thread on densitometry. It is a self-study guide (?!) in sensitometry: http://www.kodak.com/US/plugins/acrobat/en/motion/education/sensitometry_workbook.pdf -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index.htm n o lindan at ix dot netcom dot com