Project Management - Critical Path Method - Determination of Floats

 

Project Management

Critical Path Method

– DETERMINATION OF FLOATS

 

Part A: Discussion about definition of float and how to determine the different floats of the activities of a project.

Part B: YouTube link for the video on the above discussions including solution of one illustration involving –

i)      Drawing the Network Diagram,

ii)   Calculating the earliest start (ES), earliest finish (EF), latest start (LS), and latest finish (LF) of each of the activities, and

iii)   Determining the different floats of the activities of a project.

Part A

DEFINITION OF FLOATS

In project management (where management of the project involves network analysis through network diagram), while exercising control over time, resources, or cost, it is necessary to know as to what flexibility exists for scheduling the non-critical activities of the project. This flexibility that any activity has is termed as “float”. Therefore, in project management, “float”, sometimes also referred to as “slack”, is a number that indicates the amount of time a task can be delayed without impacting the subsequent tasks and the project’s overall completion time. It’s important to keep track on the floats when a project schedule is maintained for managing the project in a better way. Floats are the key pieces of the critical path method (CPM), a system used by project managers to efficiently schedule the project activities.

 

It is important to take note here that the critical activities of a project have no float. Work on non-critical activities, on the other hand, may be postponed for sometime without affecting the project duration.

 

There are four types of floats in project management as follows:

1.      Total Float,

2.      Free Float,

3.      Independent Float, and

4.      Interfering Float.

 

1.   Total Float

The total float of an activity represents the amount of time by which it can be delayed without delaying the project completion date. In other words, it refers to the amount of free time associated with an activity which can be used before, during or after the performance of this activity.

 

2.   Free Float

The free float is that part of the total float which can be used without affecting the float of the succeeding activities.

 

3.   Independent Float

The independent float of an activity is the amount of float time which can be used without affecting either the head or the tail events.

 

4.   Interfering Float

The interfering float of an activity is that part of the total float which causes a reduction in the float of the successor activities.

DETERMINATION OF FLOATS

Steps for determining the floats

Step: 1   –  Drawing the Network Diagram with durations of the activities

Step: 2   –  Identifying the Earliest Start (ES) and Latest Finish (LF) for each of the nodes of the diagram

Step: 3   –  Identifying the Earliest Start (ES), Earliest Finish (EF), Latest Start (LS), Latest Finish (LF), Head Slack and Tail Slack for each of the activities of the diagram with the help of the following chart and the formulas

 

 

Step: 4   –  Determining the floats for each of the activities

 

Total Float (three formulas)

1	LF of present activity – EF of present activity
2	LS of present activity – ES of present activity
3	LF of present activity – ES of present activity − d

 

Free Float (two formulas)

1	ES of following activity − EF of present activity
2	Total Float − Head Slack of present activity

 

Independent Float (two formulas)

1	ES of following activity − LF of preceding activity − d
2	Free Float – Tail Slack of present activity

 

Interfering Float (two formulas)

1	LF of present activity – ES of following activity
2	Head Slack of present activity

 

Part B

YouTube link for the video on the above discussions including solution of the following illustration.

Please click on the following YouTube Link:

Project Management - Critical Path Method - Determination of Floats

Critical Path Method

Determination of Floats

 

Illustration:

Information on the activities required for a project is as follows:

 

Activity	Duration (days)
1 – 2	2
1 – 3	7
1 – 4	8
2 – 5	3
3 – 5	6
3 – 6	10
3 – 7	4
4 – 6	6
5 – 7	2
6 – 8	5
7 – 8	6

You are required to –

1.         Draw the network diagram,

2.     Calculate the earliest start (ES), earliest finish (EF), latest start (LS), and latest finish (LF) of each of the activities, and

3.         Determine for each of the activities –

(i)            Head Slack,

(ii)          Tail Slack,

(iii)        Total Float,

(iv)        Free Float,

(v)          Independent Float, and

(vi)        Interfering Float.