When Cut set summation is selected as the calculation method, the gate probability is the summation of the probabilities of its cut sets. This approximation is acceptable for small failure probabilities. However, it can give gross results for fault trees with higher cut set probabilities. The probability of each cut set is calculated as the product of event probabilities. Cut set probabilities can result in a sum greater than 1.0. The frequency of occurrence is calculated by summing the frequency of occurrences of the cut sets for the gate.