we can also verify the normality of a quality feature value using an exact method using conformity tests e.g. x^2 kolmogorov-smirnov test or a test based on evaluation of the incline and kurtosis of processed values < Terek,hrnciarova 2004 > capability index cp is the rate of the potential ability of the process to ensure that a monitored quality feature lies within tolerated quality limits it can be calculated if both tolerances are specified and its value is a ratio between permitted and actual variability values regardless of where they are placed in the tolerance field index cp therefore characterises the possibilities of the process given by its variability but does not say anything about how these options are actually used this can be calculated using the formula