FORMULARY FILM DEVELOPER 23 is a metol based semi-compensating film developer similar to Kodak D-23. The developer produces negatives with low to medium contrast. Developer 23 is the favorite of Zone System users. Four rolls of film can be processed in 1 liter of Formulary 23 without replenishment. With replenishment (Formulary DK-25R, 01-0057) a total of 20 to 25 rolls of film per liter can be developed. The chemicals in this kit are used to make a working solution with a shelf life of 6 months.