Included are 12 mounted Ilford Multigrade filters. They are numbered 00 – 5 in 1/2 steps, with the lowest filter number corresponding to the softest contrast and vice versa. These are one of the most effective ways to control contrast in the darkroom
No complicated calculations are needed when changing from one filter to another. The exposure time for filters 00 – 31/2 is the same; that for filters 4 – 5 is double.