Ram: Here's one way to look at the words on page 251.
Example: you planned a project to be three months long. At the 45 day mark you only 25% complete.
So Planned vs Actual (the actual is your WPI). 50% vs 25%
The difference between both numbers is -25%. This amount is "data". You take this data and do things like make a forecast for Estimate at Completion (see page 220)
The next step for you, as the project manager, is to translate this "data" into something people can act upon. Find out what is going on and report it to your sponsor, along with what you need to fix it. Maybe you need more time, money, or resources.
Good question, by the way. WPD, WPI, WPR seems to cause many people confusion, but when you sit down and study it, it becomes quite clear.
Michael DeCicco, PMP
Moderators: Yolanda Mabutas, Ahmed Amin, Scott Gillard, Mary Kathrine Padua, ERIC BARTLETT, Gail Freedman, Kevin Nason, Steven Mudrinich, PMP, Mark Wuenscher, PMP, John Wolverton, Tracy Shagnea, PMP, Jada Garrett
This interview with Simona Fallavollita (LinkedIn Profile) was recorded at the magnificient Project Management Institute (PMI)® Global Conference 2017 in Chicago, Illinois. We discuss the how, what, why and when of the changes that are coming to the PMP exam.