scheduling basics: critical path method scheduling - nasa
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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: hsparrow@pmassoc.comwww.pmassoc.com
Since This is About Scheduling
We will start witha scheduling
awareness quiz!
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Performance Management Associates, Inc. NASA CPM Sched
Schedule Awareness Quiz
Who’s portrait is this?
Henry Laurence GanttMay 20, 1861 - November 23, 1919
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Performance Management Associates, Inc. NASA CPM Sched
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".
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Types Of Schedules
Gantt Or Bar Chart
Milestone Or Event Charts
Logic Diagrams/Networks
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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
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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
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Performance Management Associates, Inc. NASA CPM Sched
Types of PDM Relationships
Finish-to-StartStart-to-Start
Finish-to-Finish
Start-to-Finish
A BABABA BSeldom used
Leads / Lags
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Finish-to-Start
A
Dig hole
D
Plant treeFS
Activity D can start as soon as A finishes
Conventional (Default) Relationship
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Lags
APour
ConcretePatio
DHaveParty
FS + 5 Days
Activity D can start 5 days after A finishes
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Start-to-Start
ADig
Foundation
BInstall
Leveling Stakes
SS
3
1
Activity B can start as soon as A starts
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Finish-to-Finish
ISet
Appliances
JElectrical
Connections &Trimout
FF
10
5
J cannot finish until I finishes
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Task Durations (Estimates)
Developed for each activityDeveloped by best available authorityGenerally assumes normal conditions (manpower, equipment, calendar, etc.)CAUTION: - Over-Estimating Tendencies
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Performance Management Associates, Inc. NASA CPM Sched
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
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FORWARD PASSFORWARD PASS
001
A
004
D
34
01
1 May ?5
6 9
Right?!WRONG!!
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FORWARD PASSFORWARD PASS
001
A
004
D
34
ES EF ES EF
ES (Beginning of day)EF (End of day)
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FORWARD PASSFORWARD PASS
001
A
004
D
34
1 4 5 7
ES + Duration -1 = EFES (next activity) = EF (preceding activity) + 1
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Performance Management Associates, Inc. NASA CPM Sched
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
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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
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Performance Management Associates, Inc. NASA CPM Sched
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
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Activity #
Description
Duration
ES EF
LS LF
LateStart
LateFinish
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Backward PassBACKWARD PASS
007
G
013
M
106LFLSLFLS
No Lag
LS = LF – Duration +1Given “No Lag,” LF (preceding activity) = LS (succeeding activity) – 1
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Performance Management Associates, Inc. NASA CPM Sched
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
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Performance Management Associates, Inc. NASA CPM Sched
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
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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
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Performance Management Associates, Inc. NASA CPM Sched
Why Calculate The Network?
Establish ES & EF dates and project durationCalculate LF & LS dates based on project completionDefines “Float”
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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Thank you.
Harry Sparrow
829 Chiles AvenueSt. Helena, CA 94574
707-967-0420hsparrow@pmassoc.com
37Copyright © 2004 • All Rights Reserved
Performance Management Associates, Inc. NASA CPM Sched
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