Capacity Planning - 3

 Also now we are going to look into the Forward Pass, Backward pass of CPM with example

Forward Pass:

 

Early Start (ES): The earliest time a task can start. For the initial task, ES is 0.

Early Finish (EF): The earliest time a task can finish, calculated as ES + Task Duration.

Backward Pass:

 

Late Finish (LF): The latest time a task can finish without delaying the project. For the final task, LF is the project's end date.

Late Start (LS): The latest time a task can start without delaying the project, calculated as LF - Task Duration.

Slack:

 

Total Slack: The amount of time a task can be delayed without affecting the project's overall duration.

Free Slack: The amount of time a task can be delayed without affecting the start of subsequent tasks.

Example:

 

Consider a simple project with the following tasks and their estimated durations:

 

Task       Predecessor        Duration (days)

A             -              3

B             A             2

C             A             4

D            B, C        5

 

 

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Forward Pass:

 

ES(A) = 0

EF(A) = ES(A) + Duration(A) = 0 + 3 = 3

ES(B) = EF(A) = 3

EF(B) = ES(B) + Duration(B) = 3 + 2 = 5

ES(C) = EF(A) = 3

EF(C) = ES(C) + Duration(C) = 3 + 4 = 7

ES(D) = Max(EF(B), EF(C)) = 7

EF(D) = ES(D) + Duration(D) = 7 + 5 = 12

Backward Pass:

 

LF(D) = 12 (Project end date)

LS(D) = LF(D) - Duration(D) = 12 - 5 = 7

LF(B) = LS(D) = 7

LS(B) = LF(B) - Duration(B) = 7 - 2 = 5

LF(C) = LS(D) = 7

LS(C) = LF(C) - Duration(C) = 7 - 4 = 3

LF(A) = Min(LS(B), LS(C)) = 3

LS(A) = LF(A) - Duration(A) = 3 - 3 = 0

Critical Path: A-D

Project Duration: 12 days

 

By identifying the critical path, we can focus our attention on these tasks to ensure timely completion and avoid delays. Any delay in a critical path task will directly impact the overall project duration.

 

Float will be the key to decide whether the task is in Critical path are not,

A-D 12 – Duration (5) = gives 0, if the values Early Start and Late start details are matching and calculation of total float is 0 then you are calculating the right path.