CaveatWhile I am a certified PMP, I can only state my professional opinion. This website is in no other way affiliated with PMI. My caveat is simiar to the one issued in Chapter 1 of the PMBOK. It is a "body of knowledge," a functional reference that is neither complete nor all-inclusive. PMI advocates a number methodologies that originate in a variety of vocational areas. So while these techniques may seem disparate, they are considered part of the collective whole.
The explanations herein are not a replacement for the PMBOK, PM experience, study, or testing. My hope is that my explanations here will further your comprehension of these formulas and give them greater utility.