This monograph is dedicated to the newest modeling trends in debugging theory and their applications.A Hausdorff metric is chosen to evaluate the test data which are fitted to the sigmoid models. The models are tested with real data.The research in present book is a natural continuation of the following basic monographs:- N. Pavlov, A. Iliev, A. Rahnev, N. Kyurkchiev, Some software reliability models: Approximation and modeling aspects, LAP LAMBERT Academic Publishing, 2018, ISBN: 978-613-9-82805-0.- N. Pavlov, A. Iliev, A. Rahnev, N. Kyurkchiev, Nontrivial Models in Debugging Theory (Part 2), LAP LAMBERT Academic Publishing, 2018, ISBN: 978-613-9-87794-2.- V. Kyurkchiev, A. Iliev, A. Rahnev, N. Kyurkchiev, Some New Logistic Differential Models: Properties and Applications, LAP LAMBERT Academic Publishing, 2019, ISBN: 978-620-0-43442-5.