"A kappa number is the measure of the amount of lignin remaining in the pulp. As the kappa number decreases, the bleachability of pulp increases. Now, the change in the variable is thus the difference of input kappa Kappa.sub.IN and output kappa Kappa.sub.OUT, i.e. kappa reduction. An input kappa is a kappa number measured from the pulp supplied to a particular processing stage, i.e. the kappa number prior to adding a chemical dosage to the pulp in the processing stage. An output kappa is the kappa number measured from the pulp removed from the particular processing stage, i.e. the kappa number after adding the chemical dosage in the particular stage. The second method step thus provides information on the bleachability of the pulp, indicated as a kappa reduction."