Best way to calculate the Early Start/Finish and Late Start/Finish ( Rita's vs. O'reilly )

Submitted by mickcalcara on Tue, 05/18/2010 - 17:36


Hi. I learned the method of calculating the Early Start/Finish  and Late Start/Finish from Rita's PMP  prep book. I then stumbled upon this reference from the O'Reily site: http://examples.oreilly.com/9780596102340/hfpmp_ch06_errata_pp257-265.pdf These differ slighly.

In the O'Reilly document they show the similar formula as subtracting 1 from each calculation in the forward pass and adding 1 in each calculation in the backward pass as you move node to node.

Rita's approach does not do this. We simply carry the early finish to the early start of the subsequent node in the forward pass. And the backward pass we Late start and make it the Late finish in the predecessor node.

Can someone help me clarify this?  I am guessing this has to do if you start with 0 or 1.

Thanks

 

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biswasrahul

Tue, 05/18/2010 - 17:52

U guessed it right ....The difference , as it might appear is on account of the fact that while Rita may have assumed the start day as day 0, O 'reilly assumes the start day as day 1

mickcalcara

Tue, 05/18/2010 - 18:02

Thanks for the feedback.. What does the PMI support?  This does affect what an ES or LS value is. Maybe the PMP test will not ask a question regarding a specific ES or LS like this but I am just wanting to be prepared. :) thanks..

biswasrahul

Tue, 05/18/2010 - 18:07

PMI is known to test your knowledge on the application knowledge and thereby presenting you questions that test your wits and your knowledge , however , i am yet to come across situations wherein questions have ambiguity built unto themselves ....In all probability , should you be faced with a question on similar calculation , they'd provide the basis on which the calculation is to be done , i-e day 1 or day 0...In any case, should that be missing , then the answer may give you a hint ....


 


If nothing is indicated , assume the start day as day 0


 

The PMP Guru's picture

The PMP Guru

Tue, 05/18/2010 - 18:34

Hi,

I have made a Kool video on How to Calculate Early Start and Early Finish using Forward and Backward Pass and also mention this Theory which alot of people are confused whether to start from 0 or 1.

Check it please and put your feedback.

http://thepmpguru.wordpress.com/2010/05/11/early-start-early-finish-late...

Kind regards,

The PMP Guru