Forward pass is used to calculate early dates and backward pass for calculating late dates of activities in the schedule sothat we can findout floats in the activities and critical path in the schedule.

Forward Pass calculates Early Dates:

EF (early finish) = ES (early start) + DUR (activity duration) - 1

Backward Pass calculates Late Dates:

LS = LF - DUR + 1

 

Regards,

Muhammad Anjum

Stephen. The DRAG of critical activities, is new to me. The article is very informative and will be agreat start to explore & probably use the drag concept in our current and future projects. Thank you.

 

Marwan

Marwan, one additional note: the formulae shown below for Forward & Backward Passes omit perhaps the most important calculation: Critical Path Drag.  Why the most important? Because whereas float is (usually) only on activities that are off the critical path, Drag is only on activities (or constraints) that are ON the critical path! 

Drag is the measure of the time an activity (or constraint) is ADDING to the project duration.  Not only is it essential knowledge for schedule compression (and/or recovery), but, because time is money, Drag almost always has a cost (sometimes a very large cost!).  The True Cost of any CP activity is the sum of its resource cost plus its Drag Cost.  Drag Cost can be extremely useful in justifying additional resources (to reduce True Cost).

Some articles on the subject:

"The Drag Effcient: The Missing Quantification on the Critical Path", Defense AT&L Magazine:

http://www.dau.mil/pubscats/ATL%20Docs/Jan_Feb_2012/Devaux.pdf

"Scheduling Is A Drag":

http://www.projectsatwork.com/content/articles/246653.cfm

"DRAG Racing on the Critical Path":

http://www.projectsatwork.com/content/articles/234282.cfm

The two ProjectsAtWork articles require registering on the site, but it's free.

Note: Primavera does NOT compute Critical Path Drag -- but that does not mean that it is not a critical metric! If the software does not compute Drag, then the planner needs to know how to compute it "manually".  Spider Project DOES compute Drag, and IMO that fact, in and of itself, is reason to use Spider rather than Primavera.  Also, there is an add-on to MS Project 2007 and 2010 that computes Drag: the Sumatra Project Optimizer from Sumatra.com.

Fraternally in project management,

Steve the Bajan

Charlie, 

To answer that question, why not take a look at a paper that I published in the AACE International journal, Cost Engineering in 2003?  The paper is titled, “How to Befuddle a College Professor (without Really Trying)” and a copy can be found in my Published Paper Library at http://www.ronwinterconsulting.com/published.htm.  Good luck!

Here are the basic of it.

Forward computation (ES + Duration - 1 = EF)
Backward computation (LF - Duration + 1 = LS)
Total Float= LF - EF

Forward Pass:
-Task A ES is always equal to 1
-Apply forward pass formula to get EF of first task.
-Task B ES is Task A EF+1 and so on.
-For a Task with multiple predessors with different EF, adopt the largest EF+1 and so on

Backward Pass:
-EF is always equal to LF at the end or last task of the project.
-Apply backward pass formula to get LS of the last task.
-The LF of the next task is just LS of the last task - 1.
-Continue the cycle until you reach the first task.

Total Float:
TF=LF-EF

Task with zero float "Critical".

Hi, Luca.

Can you please send your presentations also to me. I was today on the way to find on the internet some data about it. And I have find this wonderfull webpage. It’s really great. I’m now Guest. I waiting only of my password and ID.

I will be very happy, if you send it also to me.

Thanks a Lot.

My e-mail adress is: akocak4@yahoo.de

Hi Luca,

If you could also e-mail me your presentations, i would be really greatful to you.

stauqeer@ajes.ae

Hi,
is it possible for you to email the powerpoint slides to me as well please?
My email is hulahoops92@yahoo.com
looking forward,
Hamish

Wilfred,

Kabayan. give me an email, i could help you better through email. I’m not surprised that you got a not so detailed answers because your question is really very basic. Email me at sadeleon@tollways.net.

Hope to hear from you and extend you some help.

No problem, It is always good to ask rather than keeping quiet.

Please get some fundametals first.P3 is a just a tool, but all the input must come from us first.

Best of luck

Dinesh

This book explains it pretty well:
Project Management for Construction

Bernard Ertl
InterPlan Systems Inc. - Project Management Software, Project Planning Software

Hi,

This is very basic for planning to find out longest path and to determine the float.

P3 will actually do it for you automatically all these calculations.

Even P3 does it all for you,you should know this other wise you can not understand the significance of CPM and the float in your plan.

I suggest get some book on planning and read it.It is a simple concept and not difficult to understand.

Best of luck

Dinesh