If negative filter values are present in the pack, add (by
calculation) C, M, and Y "neutral density" equal to the largest negative
filter. In this way, one of the three filters will become zero. Look up
the neutral density factor in section A of the figure 5-3.
Neutral density factor
Since negative filter values are present in the pack, add 10
neutral density (+10C, +10M, and +10Y) to these values.
Example: Step 3A.