In Sect. 5.4.3, we discussed four quality criteria: fitness, precision, generalization, and simplicity. These were illustrated using Fig. 5.24. In this figure, one event log is given and four process models are shown. For each of these models, a subjective judgment is given with respect to the four quality criteria. As the models are rather extreme, the scores for the various quality criteria are evident. However, in a more realistic setting it is much more difficult to judge the quality of a model. This section shows how the notion of fitness can be quantified. Fitness measures “the proportion of behavior in the event log possible according to the model”. Of the four quality criteria, fitness is most related to conformance.