Genorm output. A: Expression stability values (M) of the candidate normalization factors, during the stepwise exclusion of least stable normalization factors. Candidate normalization factors are ranked from the least stable to the most stable (left to right). B: Determination of the optimal number of normalization factors to be used, based on the analysis of pairwise variation (V) between normalization factors. A low value of V means that the inclusion of an additional normalization factor would not lead to a increase in stability.