SCHEDULING BASICS: Critical Path Method Scheduling · PDF fileSCHEDULING BASICS: Critical Path...

SCHEDULING BASICS:Critical Path Method Scheduling

presented for

First Annual NASA Project Management Conference

Meeting the PM Challenge

College Park, MDMarch 30-31, 2004

presented by

Harry Sparrow829 Chiles Avenue • St. Helena CA • (707) 967-0420

Fax: (707) 967-0504 • E-mail: [email protected]

Since This is About Scheduling

We will start witha scheduling

awareness quiz!

2Copyright © 2004 • All Rights Reserved

Performance Management Associates, Inc. NASA CPM Sched

Schedule Awareness Quiz

Who’s portrait is this?

Henry Laurence GanttMay 20, 1861 - November 23, 1919



Schedule Awareness Quiz

What’s this a picture of?

This is a picture of an ancient Roman street sign which was placed every mile along the highway. It told the traveler how far he had gone and how much farther his destination was. It was commonly known as a "Milestone".



Types Of Schedules

Gantt Or Bar Chart

Milestone Or Event Charts

Logic Diagrams/Networks



NetworksComposite refinement of charting techniquesStresses logic/interdependenciesEffective for complex one-of-a-kind projects

Graphical representation of project showing interrelationships of activitiesWhen time estimates and computations are added – becomes project schedule



Precedence Diagramming Method (PDM)

B

C

E

F

A

D

H I

G

J

Developed at Stanford UniversityAlso called “Activity-On-Node”More flexibility in showing relationship



Types of PDM Relationships

Finish-to-StartStart-to-Start

Finish-to-Finish

Start-to-Finish

A BABABA BSeldom used

Leads / Lags



Finish-to-Start

A

Dig hole

D

Plant treeFS

Activity D can start as soon as A finishes

Conventional (Default) Relationship



Lags

APour

ConcretePatio

DHaveParty

FS + 5 Days

Activity D can start 5 days after A finishes



Start-to-Start

ADig

Foundation

BInstall

Leveling Stakes

SS

3

1

Activity B can start as soon as A starts



Finish-to-Finish

ISet

Appliances

JElectrical

Connections &Trimout

FF

10

5

J cannot finish until I finishes



Task Durations (Estimates)

Developed for each activityDeveloped by best available authorityGenerally assumes normal conditions (manpower, equipment, calendar, etc.)CAUTION: - Over-Estimating Tendencies



Network A

M/S

0

ProjectStart

3B

10E

4A

3D

C

4

F

8

G

6

M

10

ProjectCompleted0

M/S

4H

5L

4K

3J

2I

PROJECT LENGTH?14

Copyright © 2004 • All Rights ReservedPerformance Management Associates, Inc. NASA CPM Sched

Forward PassFrom project start to finish, calculate the earliest that each activity can start and finish according to the logical sequence of work and the duration of each activity

EARLY DATES

Yields project duration



FORWARD PASSFORWARD PASS

001

A

004

D

34

01

1 May ?5

6 9

Right?!WRONG!!




001

A

004

D

34

ES EF ES EF

ES (Beginning of day)EF (End of day)




001

A

004

D

34

1 4 5 7

ES + Duration -1 = EFES (next activity) = EF (preceding activity) + 1



Forward Pass

M/S

0

000ProjectStart 3

002B

10

005E

4

001A

3

004D

003C

4

006F

8

007G

6

013M

10

014Project

Completed0

M/S

4

008H

5

012L

4

011K

3

010J

2

009I

1 0 1 3 4 13

1 4 5 7

1 4 125 1914 2920

2930

14 17 18 22

19 2216 1814 15

FORWARD PASS



Multiple Paths

008

H

4005

E

10

4 13

14 17

004

D

3

5 7

FORWARD PASS

Always take the “latest” date (or largest number)

FORWARD PASS



Backward PassWorking backward from project finish to start, calculate the latest that each task must start and finish in order to meet the end date.

LATE DATES

Yields when the project must start to meet the latest acceptable completion date.

LATE DATES



Activity #

Description

Duration

ES EF

LS LF

LateStart

LateFinish



Backward PassBACKWARD PASS

007

G

013

M

106LFLSLFLS

No Lag

LS = LF – Duration +1Given “No Lag,” LF (preceding activity) = LS (succeeding activity) – 1



Network A

A D

B

C

E

F G

I

H

J

L

K

ProjectCompleted0

M/S

Project Start

M/S

0 3

4 3

4

2

5

43

10

4 8 6

1 4

1 0

5 7

14 17 18 22

1 3 4 13

14 15 16 18 19 22

30 29

1 4 5 12 14 19

30 291 0

14 17 18 20

21 24 25 29

21 22 23 25 26 29

1 3 4 13

2 5 6 13 14 19

M10

20 29

20 29

000

001 004

002

003

005

006 007

009

008

010

012

011

014

013



Backward Pass

M/S

0

1 0000

ProjectStart 3

1 3002

B10

4 13005

E

4

1 4001

A3

5 7004

D

1 4003

C4

12006

F8

5 19007

G6

14 29013

M10

20

29014

ProjectCompleted0

30 M/S

4

14 17008

H5

18 22012

L

4

19 22011

K3

16 18010

J2

14 15009

I

1 0 1 3 4 13

14 17 18 20

21 24 25 29

2321 22

2 5 136 1914 2920

2930

26 2925

BACKWARD PASS



Multiple Paths

010

J

3

16 18

BACKWARD PASS

005

I

2

14 15

Always take the “earliest” date (or smallest number)

012

L

5

18 22

22

25 29

23 25

BACKWARD PASS



Why Calculate The Network?

Establish ES & EF dates and project durationCalculate LF & LS dates based on project completionDefines “Float”



Total Float(Leeway Or Slack)

Amount of time an activity can be delayed before it impacts Project CompletionCalculated by comparing LF to EF

= 13 days "Float"

001

A

4

1 4

1714

Also called Path/Shared Float



Total Float

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

LF

EFES

LS

A A

Total Float for Activity A



Network A Total Float

A D

B

C

E

F G

I

H

J

L

K

ProjectCompleted0

M/S

Project Start

M/S

0 3

4 3

4

2

5

43

10

4 8 6

1 4

1 0

5 7

14 17 18 22

1 3 4 13

14 15 16 18 19 22

30 29

1 4 5 12 14 19

30 291 0

14 17 18 20

21 24 25 29

21 22 23 25 26 29

1 3 4 13

2 5 6 13 14 19

M10

20 29

20 29

000

001 004

002

003

005

006 007

009

008

010

012

011

014

0130

7

7

77

13 137

0 0

1 1 0



Network A

M/S

0

1 0000

ProjectStart

3

1 3002

B10

4 13005

E

4

1 4001

A3

5 7004

D

1 4003

C

4

12006

F

8

5 19007

G

6

14 29013

M

10

20

29014

ProjectCompleted0

30 M/S

4

14 17008

H5

18 22012

L

4

19 22011

K3

16 18010

J2

14 15009

I

1 0 1 3 4 13

14 17 18 20

2 5 136 1914 2920

2930

21 24 25 29

26 2923 2521 22

Critical Path



Critical Path

Longest path of logically related activities through the network which has the “least” Total Float.Defines project duration.Network A Path:

B E G M3 10 6 10+ + + = 29 days



Activity (Free) FloatAmount of time an activity can be delayed before it impacts any succeeding activity

6 days "Free Float"

3

D

5 7

H

14 17

4

004 008



NETWORK A FREE FLOAT

A D

B

C

E

F G

I

H

J

L

K

ProjectCompleted0

M/S

Project Start

M/S

0 3

4 3

4

2

5

43

10

4 8 6

1 4

1 0

5 7

14 17 18 22

1 3 4 13

14 15 16 18 19 22

30 29

1 4 5 12 14 19

30 291 0

14 17 18 20

21 24 25 29

21 22 23 25 26 29

1 3 4 13

2 5 6 13 14 19

M10

20 29

20 29

000

001 004

002

003

005

006 007

009

008

010

012

011

014

0130

7

7

77

13 13

7

0 0

1 1 0

0

0

0

0

1

6

0

0

0

0 7

7

0

Critical Path



Planning/Scheduling Process

Defines the activities involved in the project, their logical sequence, and their interrelationship.

Places the project and each of its activities in a workable timetable.

PLANNING(Think)

SCHEDULING(Do it)



With Calendar Applied

M/S

0

000ProjectStart

3

002

B10

005

E

4

001

A3

004

D

003

C

4

006

F

8

007

G

6

013

M

10

014Project

Completed0

M/S

4

008

H5

012

L

4

011

K3

010

J2

009

I

1 May 4 May

18 May 23 May

1 May 3 May

1 May 3 May

1 May 4 May

2 May 7 May

7 May 9 May

24 May 29 May

4 May 17 May

4 May 17 May

7 May 16 May

8 May 17 May

18 May 23 May

30 May 4 Jun

18 May 21 May

30 May 31 May

18 May 25 May

18 May 25 May

22 May 24 May

1 Jun 5 Jun

24 May 31 May

5 Jun 11 Jun

25 May 31 May

6 Jun 11 Jun

29 May 11 Jun

29 May 11 Jun

1 May 11 June



Thank you.

Harry Sparrow

829 Chiles AvenueSt. Helena, CA 94574

[email protected]



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