01. critical path analysis - latest jan 09
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HND UNIT 1
BUSINESS MANAGEMENT TECHNIQUES
CRITICAL PATH ANALYSIS
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Critical path analysis (CPA) is a powerful tool
to help you schedule and manage complex
projects.
History
Developed in the 1950s to control large
defence projects and has been used eversince.
CRITICAL PATH ANALYSIS
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Advantages of CPA over Gantt Charts
Formally identifies tasks, which must be completed ontime for the whole project to be completed on time.
Identifies tasks, which can be delayed for a while if
resources need to be allocated to catch up on missed
tasks.
Identifies the minimum length of time to complete a
project.
It helps to identify which tasks need to be accelerated if
you need to run an accelerated programme.
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Disadvantages of CPA over Gantt Charts
Relation of tasks to time is not
immediately obvious i.e. no timeline.
Therefore CPA charts are more difficult to
understand if you are not familiar with
technique.
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Activity
Is a task or function that consumes time and other
resources.
Event
Consumes no resources, especially no time. An event can
be considered to represent a point in time or the
representation of the status of a project at a particular
instance i.e. project starts.
CPA chart nomenclature
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Drawing a CPA chart
List all activities in the plan
Show the earliest start date
Estimate the length of time for each task
Determine whether the tasks are parallel or
sequential. If sequential show what task they are
dependent upon.
Plot the activities in a graphical depiction of the
project i.e. tasks that make up the project andthe logical relationships between them
represented by symbols
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There are two types of logic diagrams:-
Types of Diagram
Circle and arrow.
Precedence diagrams.
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Arrow Diagrams
Diagram is made out of arrows and nodes plusnumbers and letters for calculation and labelling
purposes.
The arrows represent the actual activity of task.
The nodes represent the point in time (event)
when activities start and finish.
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Precedence Diagrams
Activities are shown as nodes. Arrowsrepresent activity links or logical
relationships.
Activity links can have lead times i.e. paint
drying etc, links consume no other resource
than time.
Lead times can be zero positive or
negative.
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Diagram differences
The two diagrams are fundamentallydifferent in the methods of graphicallyrepresentation but they depict the
same information.
However precedence diagrams areconsidered easier to develop and
understand.
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EARLIEST
START
LATESTSTART
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATHSLACK TIME LATESTFINISH
PRECEDENT DIAGRAM
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EARLIEST
START
LATESTSTART
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATHSLACK TIME LATESTFINISH
PRECEDENT DIAGRAM
INSERT DESCRIPTION OR NUMERICAL VALUES
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PRECEDENT DIAGRAM
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
FINISH TO START - MOST COMMON
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EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
EARLIESTSTART
LATESTSTART
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATESTFINISH
START TO START
PRECEDENT DIAGRAM
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EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
START TO FINISH
PRECEDENT DIAGRAM
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EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIME
LATEST
FINISHFINISH TO
FINISH
PRECEDENT DIAGRAM
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EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
FINISH TO START WITH PRECEDENT
PRECEDENT
TIME
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PRECEDENT DIAGRAM
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EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISHEARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
PRECEDENT DIAGRAM
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
EARLIEST
START
LATEST
START
DURATION
ACTIVITY DESCRIPTION
EARLIEST
FINISH
CRITICAL PATH
SLACK TIMELATEST
FINISH
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Early start (ES) - the point in time that all preceding activities
have been completed.
Early finish (EF) - the earliest that all work started with an early
start can be completed.
EF = ES + D
Late finish (LF) - the point in time that all work involved in theactivity must be completed in order to avoid delaying subsequent
activities.
Late Start (LS) - the point in time by which an activity must be
started in order to avoid delay to following activities. LS = LF-D
Project Duration (D) - is the aggregate combination of all the
activities along the critical path of the project.
Activity Times
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Is the path representing the combination of
activities any one which delayed will cause a
delay to the project.
It is the longest time through the network.
Critical activities have zero total float.
Critical path
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Total float
Total float or slack time is the amount of timeby which the start or finish of an activity canbe delayed without delaying the projectcompletion.
TF = ES LF D, or
TF = LF EF, or
TF = LS - ES (PREFERRED OPTION)
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Free float
The maximum amount of time that anactivity can be delayed beyond its earlystart without delaying the early start ofany other activity immediately following
that activity.
FF = ES succeeding - EF preceding
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Networks have to be solved in two passesa forward pass and a backward pass.
Dangling activities - all activities should
have at least one preceding activity andat least one succeeding activity except
from start and finish.
Lines CANNOTcross one another and
should minimise clutter.
Some Rules of Logic Diagrams
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Time - working days i.e. overall duration
Man days - days people work
Paint drying days
Money costs sales and profit
Raw materials
Actual numbers of people
Estimating Resources
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Man-days
Are the number of people performing an
activity multiplied by the working day or
duration.
The number of days that an activity willtake until completed.
To identify these requirements a numberof estimating techniques must be used.
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Comparative estimates - use data fromcomparable projects i.e. against figures
recorded cost +/-15%
Feasibility estimates - total quotations foreach component part.
i.e. you can calculate how much paint a
ship will require to be fully coated with a
primer, base coat and top coat.
ESTIMATING TECHNIQUES
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ESTIMATING TECHNIQUES
Ballpark estimates - are based on judgementand luck. +/- 25%.
Percentage estimates - are models based on
progress to date compared with otherprojects.
i.e. - At this point in time I have spent 10 and
I am 10% through the project hence projectcosts are 100.
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Ballpark
Twice the optimistic plus four times
pessimistic add the most likely and divide by 7
Weight time estimates
Team experience/size
if very experienced reduce estimates by 10%
If limited experience add 10%
Rules of
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Rules of
Customer support/understanding
Great support reduce by 10%Limited support add 10%
Little support add 20%
Novelty of project
If some new add 10%If all new add 20%
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Rules of
Number of customers involved or number of
organisations
If 2 add 10%
If 3-4 add 20%
If 5 or more add 40%
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Percentage of time spent on other work by ateam member
10-30% add 10% to estimates
30-50% add 20%More than 50% add 30%
Project plan complexity
If simple reduce by 10%
If very complex add 10%
Rules of
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Is a variation on critical path analysis. It takes a moresceptical viewof time estimated for each stage.
Time for a project stage:-
(shortest time + 4) x (likely time + longest time)6
It helps to refocus timescale needed, by giving a
reasonable estimation of time rather than theunrealistically short timescale normally
assumed/DEMANDED.
Programme Evaluation and Review Technique (PERT)
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SETTING OUT THE ANALYSIS
ANDDUMMY ACTIVITIES
SETTING OUT THE ANALYSIS AND
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Layout a rough diagram of the project/Task
flow.
Ensure that you have the order of projectactivity shown in the correct order.
Label activities A,B etc.
In an exam you will be given numerical
values.
SETTING OUT THE ANALYSIS ANDDUMMY ACTIVITIES
SETTING OUT THE ANALYSIS AND
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SETTING OUT THE ANALYSIS ANDDUMMY ACTIVITIES
Connect activities together using flow lines
REMEMBER that flow lines cannot cross.
Think of the analysis as a pipeline diagram or
piping system pumping manyDIFFERENTtypes
of fluid.
Different fluids cannot travel in the same pipe
andcannot cross connect.
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Start with a START( EVENT) box and finish
with a FINISH(EVENT) box
If lines cross connect use a DUMMYbox, an
EVENTblank box, to connect the paths.
SETTING OUT THE ANALYSIS ANDDUMMY ACTIVITIES
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SETTING OUT THE ANALYSIS ANDDUMMY ACTIVITIES
Analyze the project time thus:-
Start box
Box AStart time plus duration =finish time
Box B
Start time = previous box finish time.Finish time = start time plus duration etc.
SETTING OUT THE ANALYSIS AND
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NOTESometimes between boxes you have a PRECEDENCE
time: this refers to a SLACK time period that occurs
after an ACTIVITY/Task has finished
Typically this could be: paint drying, concrete setting,
waiting for tides etc.
This precedent must be added on to the end of the
previous activity in order to evaluate total time.
When more than one previous activity connect to the
next box, then the HIGHEST finish time becomes the
next start time.
SETTING OUT THE ANALYSIS ANDDUMMY ACTIVITIES
ANALYSIS
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Project time is evaluated by ADDING duration time,
going from left to right, to arrive at the highest number
for evaluating the project time.
LOWEST + DURATION = HIGHEST
CRITICAL PATH ANALYSIS is established by moving fromright to left and using the highest number as a start
point and SUBTRACTING duration time to arrive at
LATEST START TIME and thus assess SLACK TIME.
When SLACK Time is ZERO, then this activity is CRITICAL
and you have found a CRITICAL path.
ANALYSIS
ACTIVITY DESCRIPTION OF ACTIVITY IMMEDIATE PREDECESSOR DURATION IN DAYS
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ACTIVITY DESCRIPTION OF ACTIVITY IMMEDIATE PREDECESSOR DURATION IN DAYS
A Conduct feasibility study No 3
B Find potential customer for existing car A 14
C List possible models A 1
D Research all possible models C 3
E Conduct interviews with mechanics C 1
F Collect dealer propaganda C 2
G Compile and organise all pertinent information D, E, F 1
H Choose top three models G 1
I Test drive all three choices H 3
J Gather warranty and financing information H 2
K Choose one car I, J 2
L Compare dealers and choose dealer K 2
M Select colour and goodies options L 4
N Test drive first choice again-CHECK IMPRESSIONS L 1
O Purchase new car B, M, N 3
CONCLUSION
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Critical Path Analysis is an effective and powerful
method of assessing:-
CONCLUSION
What tasks must be carr ied out.
Where paral lel activity can be performed.
The shortest time in which you can complete a project .
Resources needed to execute a project.
The sequence of activities, schedul ing and timings involved.
Task pri ori ties- reallocation of resources.
The most eff icient way of shortening time on urgent projects.
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CONCLUSION
An effective Critical Path Analysis can make
the difference between success and failure on
complex projects.
It can be very useful for assessing the
importance of problems faced during the
implementation of the plan.
CAR PURCHASE
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ACTIVITY DESCRIPTION OF ACTIVITY IMMEDIATE PREDECESSOR DURATION IN DAYS
A Conduct feasibility study No 3
B Find potential customer for existing car A 14
C List possible models A 1
D Research all possible models C 3
E Conduct interviews with mechanics C 1
F Collect dealer propaganda C 2
G Compile and organise all pertinent information D, E, F 1
H Choose top three models G 1
I Test drive all three choices H 3
J Gather warranty and financing information H 2
K Choose one car I, J 2
L Compare dealers and choose dealer K 2
M Select colour and goodies options L 4
N Test drive first choice again-CHECK IMPRESSIONS L 1
O Purchase new car B, M, N 3
CONSTRUCTION PROBLEMWORKED EXAMPLE 2
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CONSTRUCTION PROBLEM
ACTIVITY DURATION WEEKS PRECEDING ACTIVITIES
A 4
B 6
C 5
D 5 A B
E 7 A B
F 4 A B C
G 3 B C
H 7 B C
J 6 D E
K 7 F
L 3 F G
M 5 H
N 4 J
P 5 K Q
Q 7 L M
R 2 N P
S 4 P
PROBLEM 3
SHIP PROJECTWORKED EXAMPLE ANSWER 3 INTRO TO MS PROJECT
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SHIP PROJECT
ACTIVITY
IDENTITY
PRECEDING ACTIVITIES PRECEDENCE LINES ACTIVITY DURATION
WEEKS
PRECEDENCE TIMES
A 5 0
B A START/START 10 4
C B FINISH/FINISH 15 5D A FINISH/START 6 0
E B FINISH/START 3 2
D START/START 4
D FINISH/FINISH 5
F C FINISH/START 10 2
E START/START 3
E FINISH/FINISH 2
G D FINISH/START 5 2
Y START/START 0
Y FINISH/FINISH 0
H E FINISH/START 8 3
J F FINISH/START 3 0
X A START/START 7 3
Y X FINISH/START 7 6
Z Y FINISH/START 8 9
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ACTIVITY DURATION
DAYS
PRECEDING ACTIVITIES FIXED PRECEDENCE
TIMES
START
A 7
B 2
C 15 A,B 1
D 8 A,B 4
E 10 D 2
F 2 E
G 5 E
H 8 E 4
I 2 H
J 3 I
FINISH
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ACTIVITY DURATION
DAYS
PRECEDING ACTIVITIES FIXED PRECEDENCE
TIMES
START
A 7
B 2
C 15 A,B 0
D 8 C 2
E 10 D 5
F 2 C 3
G 5 F 0
H 8 D 0
I 2 H 0
J 3 G 3
FINISH
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ACTIVITY DURATION
DAYS
PRECEDING ACTIVITIES FIXED PRECEDENCE
TIMES
START
A 7
B 2
C 15 B 0
D 8 C,A 2
E 10 D 5
F 2 E 3
G 5 F 0
H 8 0
I 2 G 0
J 3 D 3
Z 3 H, I 4
FINISH
C P h CPA
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Car Purchase CPA
CRITICAL PATH = C D G H I K LM -O
Start A
330
300
C
413
403
B
17143
2036
D
734
704
EE
514
726
F
624
715
G
817
807
H
918
908
I
1239
1209
J
1129
12110
K
14212
14012
L
16214
16014
M
20416
20016
N
17116
20319
0
23320
23020
Finish
23023
23023
0 0 0
000
Total Float = LS ES = 10 days
Construction Project
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CRITICAL PATH = BH M Q PS
Start
A
440
1177
C
550
611
B
660
600
D
1156
221117
EE
1376
22915
F
1046
15511
G
936
15612
H
1376
1306
Q
25718
25018
J
19613
28922
K
17710
25818
L
13310
18515
M
18513
18013
N
23419
32928
P
30525
30025 Finish
34034
34034
0 0 0
000
Dummy
606
11011
Dummy
606
606
R
32230
34232
S
34430
34030
j