According to the PM Formulas booklet, page 7, it states how that there are two approaches for calculating ES, EF, LS and LF and how you can use the network diagram starting at either "0" or at "1", and that both of these methods will yield the same results.
However, that is not the case, depending on what is being asked. Please look at the attached .ppt file to see how using the different methods will yield different numbers for the boxes.
For example, if you were ONLY given the float activity box information:
ES = 6
DUR = 2
And asked to provide the EF, if you used the "0" method, you would end up with 8. (EF = ES + DUR)
And asked to provide the EF, if you used the "1" method, you would end up with 7. (EF = ES + DUR - 1)
Since the "0" method puts the successor's ES as the same day as the predecesor's EF, the ES numbers will always be different than using the "1" method. This isn't such a problem (except for the point made above) really, until you get to float activities, where everything breaks down. Again, see the example.
The "1" method puts the successor's ES as the day after the predecesor's EF.
I would like to see how Neelesh did this, because this demonstrates that both methods are not equal. Unless I am completely missing something...
Last Edit: by Joe Muccianti. Reason: Original attached file missing? Adding again.
I remember encountering this same dilemma when I was studying for my PMP examination.
First, I recommend a consistent approach to the critical path formula. I add the duration from the Early Start and subtract 1. This gives me Early Finish. This math is associated when performing forward pass and backward pass, but in reverse.. I recommend looking into other critical path study resources such as Head First.
Second, understanding the purpose of critical path is important. CPM is just one several techniques you can use in Time Management performance reviews. Others include trend analysis, critical chain method, and earned value management
•Remember the critical path is the longest path on the project schedule with zero or negative float
–If there are variances in critical path tasks, your schedule is likely at risk
–Examining critical path tasks, or those near a critical path task, can help alert you to schedule risk. See attached file from the pmlessonslearned.com and yahoo group that I'm a part of.
Lastly, I did not see your attachment. If you could, please try posting it again.
Your attachment opened up. I've seen something similar in other CPM training aids.
I want to say the PMI standard has swayed toward the starting at "1" method for determing CP in Forward and Backward pass. In many of my examples that I used during my study time, that is the technique I used.
I think others on this forum can confirm or deny my assumption.
In the absence of further guidance, I recommend you use the "1" method. But remember, if you come across a diagram on an exam with "0", then you'll know what math to use.
Michael DeCicco, PMP
I'm thinking the same thing. Use the "1" method. This is what is shown in the PMBoK guide. I originally studied that method, then switched to the "0" method because it was easier. I mean, why muddle with extra steps that could cause stupid mistakes during a crammed 4 hour exam, right?! But if we compare the two float tasks, one can clearly see that without any other context, one could easily answer the question wrong, especially when the answers might be close together: A) 5 days, 6 days, C) 7 days, etc.
So I think that since I know both methods, I'll now stick with the "1" method.
What is concerning to me is that both methods are taught for the exam, but both will yield different results, as demonstrated. However, for real-world practical use, I'm not sure it really makes all that much difference, since the "interpretation" is what is key. But for the exam, interpretation is not an option, because context is not provided, and the difference is between the right answer and the wrong answer.
I would love to see how this other person mentioned in the Formulas guide proved that both methods yield the exact same results because I just can't see how it would be accomplished.
I posted a reply to this over a day ago and apparently it did make it through the screening process and I'm not sure why.
I don't recall precisely what I repsonded the other day, but I think the jist of it was that I am going to use the "1" method since it aligns with the PMBoK guide.
Secondly, as my PowerPoint shows, the answers are clearly different and if you are only provided activities without context on the exam and asked for an answer, you can obviously pick the wrong one when the answers may be A) 5 days, 6 days, C) 7 days, D) 11 days. If you are one off, you still get it wrong. It doesn't matter what the real world application is, it only matters that the correct answer according to the methodolgy chosen is selected.
In any case, I would still like to see it demonstrated Neelesh Pandey, PMP, because this model shows otherwise. (Referencing the Formulas for Success Guide (if anyone else has purchased that through PM PrepCast) it is on page 7.
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.