I would agree that it is an excellent professional reference book. I do not think it is necessary for the Mechanical PE Exam. When I passed the test, I did it with the MERM, Shigley's, and the Machinery's Handbook. I didn't use the Machinery's Handbook. Mark's is great when you don't have sufficient information to solve the problem, but the MERM covers most of this material pretty well in the appendices with regards to what questions are going to be asked on the exam.