Network Analysis

[Glenn]

Some more links

www.mindtools.com/critpath.html

Critical Path Analysis
and PERT Charts
Planning and Scheduling Complex Projects
Related variants: AOA or Activity-on-Arc or Activity-on-Arrow Diagrams

Critical Path Analysis and PERT are powerful tools that help you to schedule and manage complex projects. They were developed in the 1950s to control large defense projects, and have been used routinely since then.

As with Gantt Charts, Critical Path Analysis (CPA) helps you to plan all tasks that must be completed as part of a project. They act as the basis both for preparation of a schedule, and of resource planning. When you are managing a project, they allow you to monitor achievement of project goals, and help you to see where remedial action needs to be taken to get a project back on course.

The benefit of using CPA over Gantt Charts is that Critical Path Analysis formally identifies tasks which must be completed on time for the whole project to be completed on time (these are the tasks on the critical path), and also identifies tasks which can be delayed for a while, if resources need to be redeployed to catch up elsewhere.

The disadvantage of CPA is that the relation of tasks to time is not as immediately obvious as with Gantt Charts. This can make them more difficult to understand.

How to use the tool:
As with Gantt Charts, the essential concept behind Critical Path Analysis is that you cannot start some activities until others are finished. These activities need to be completed in a sequence, with each stage being more-or-less completed before the next stage can begin. These are 'sequential' activities.

Other activities are not dependent on completion of any other tasks. You can do these at any time, before or after a particular stage is reached. These are non-dependent or 'parallel' tasks.

Drawing a Critical Path Analysis Chart
Use the following steps to draw a CPA Chart:

1. List all activities in the plan
For each activity, show the earliest start date, the estimated length of time it will take, and whether it is parallel or sequential. If tasks are sequential, show which stage they depend on.

So that you can compare Critical Path Analysis with use of Gantt Charts, we'll base our example, shown in figure 1 below:

Figure 1. Task List: Planning a custom-written computer project
NB: The start week shows when resources become available. Whether a task is parallel or sequential depends largely on context.

Task Possible start Length Type Dependent on...

1. High level analysis week 1 5 days sequential
2. Selection of hardware platform week 1 1 day sequential 1
3. Installation and commissioning of hardware week 3 2 weeks parallel 2
4. Detailed analysis of core modules week 1 2 weeks sequential 1
5. Detailed analysis of supporting utilities week 1 2 weeks sequential 4
6. Programming of core modules week 4 3 weeks sequential 4
7. Programming of supporting modules week 4 3 weeks sequential 5
8. Quality assurance of core modules week 5 1 week sequential 6
9. Quality assurance of supporting modules week 5 1 week sequential 7
10.Core module training week 7 1 day parallel 6
11.Development of accounting reporting week 6 1 week parallel 5
12.Development of management reporting week 6 1 week parallel 5
13.Development of management analysis week 6 2 weeks sequential 5
14.Detailed training week 7 1 week sequential 1-13
15.Documentation week 4 2 weeks parallel 13

2. Plot the activities as a circle and arrow diagram
Critical Path Analyses are presented using circle and arrow diagrams.

In these, circles show events within the project, such as the start and finish of tasks. Circles are normally numbered to allow you to identify them.

An arrow running between two event circles shows the activity needed to complete that task. A description of the task is written underneath the arrow. The length of the task is shown above it. By convention, all arrows run left to right.

An example of a very simple diagram is shown below:




This shows the start event (circle 1), and the completion of the 'High Level Analysis' task (circle 2). The arrow between them shows the activity of carrying out the High Level Analysis. This activity should take 1 week.

Where one activity cannot start until another has been completed, we start the arrow for the dependent activity at the completion event circle of the previous activity. An example of this is shown below:




Here the activities of 'Selecting Hardware' and 'Core Module Analysis' cannot be started until 'High Level Analysis' has been completed. This diagram also brings out a number of other important points:

Within Critical Path Analysis, we refer to activities by the numbers in the circles at each end. For example, the task 'Core Module Analysis' would be called 'activity 2 to 3'. 'Select Hardware' would be 'activity 2 to 4'.


Activities are not drawn to scale. In the diagram above, activities are 1 week long, 2 weeks long, and 1 day long. Arrows in this case are all the same length.


In the example above, you can see numbers above the circles. These show the earliest possible time that this stage in the project will be reached. Here units are whole weeks.
A different case is shown below:




Here activity 6 to 7 cannot start until the other three activities (12 to 6, 5 to 6 and 9 to 6) have been completed.

See figure 5 for the full circle and arrow diagram for the computer project we are using as an example.


Click here to see the full Critical Path Diagram

This shows all the activities that will take place as part of the project. Notice that each event circle has a figure below it as well as a figure above. This shows the latest time that it can be reached with the project still being completed in the minimum time possible. You can calculate this by starting at the last event (in this case number 7), and working backwards.

You can see that event 4 can be completed any time between 1.2 weeks in and 7.8 weeks in. The timing of this event is not critical. Events 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6 and 6 to 7 must be started and completed on time if the project is to be completed in 10 weeks. This is the 'critical path' - these activities must be managed very closely to ensure that activities are completed on time. If jobs on the critical path slip, immediate action should be taken to get the project back on schedule. Otherwise completion of the whole project will slip.

'Crash Action'
You may find that you need to complete a project earlier than your Critical Path Analysis indicates is possible. In this case you need to take action to reduce the length of time spent on project stages.

You could pile resources into every project activity to bring down time spent on each. This would probably consume huge additional resources.

A more efficient way of doing this would be to look only at activities on the critical path.

As an example, it may be necessary to complete the computer project in figure 5 in 8 weeks rather than 10 weeks. In this case you could look at using two analysts in steps '2 to 3' and '3 to 4', and two programmers instead of one in step '4 to 5'. This would shorten the project by two weeks, but would raise the project cost - doubling resources at any stage often only improves productivity by, say, 50%. This occurs as time spent on coordinating the project consumes time gained by increasing resource.

Note that in this example, shortening the project by two weeks brings activities '3 to 11', '11 to 12' and '12 to 6' onto the critical path as well.

As with Gantt Charts, in practice project managers tend to use software tools like Microsoft Project to create CPA Charts. Not only do these make them easier to draw, they also make modification of plans easier and provide facilities for monitoring progress against plans.

PERT (Program Evaluation and Review Technique)
PERT is a variation on Critical Path Analysis that takes a slightly more skeptical view of time estimates made for each project stage. To use it, estimate the shortest possible time each activity will take, the most likely length of time, and the longest time that might be taken if the activity takes longer than expected.

Use the formula below to calculate the time to use for each project stage:

shortest time + 4 x likely time + longest time
-----------------------------------------------------------
6

This helps to bias time estimates away from the unrealistically short time-scales normally assumed.

Key points:
Critical Path Analysis is an effective and powerful method of assessing:

What tasks must be carried out.
Where parallel activity can be performed.
The shortest time in which you can complete a project.
Resources needed to execute a project.
The sequence of activities, scheduling and timings involved.
Task priorities.
The most efficient way of shortening time on urgent projects.
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.

PERT is a variant of Critical Path Analysis that takes a more skeptical view of the time needed to complete each project stage.

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Management in Our Community!

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[Glenn]

Another sourse see link to connect to various paths mentioned.

en.wikipedia.org/wiki/Critical_path

From Wikipedia, the free encyclopedia
(Redirected from Critical path)
Jump to: navigation, search
Critical Path may refer to:

Critical path method, an algorithm for scheduling of activities
Critical Path (book) by Buckminster Fuller
Critical Path (video game), an interactive movie computer game

[Glenn]

Yey another

tutor2u.net/business/production/critical-path-analysis.htm
Critical Path Analysis CPA (Network Analysis)
Critical Path Analysis (CPA) is a project management tool that:

Sets out all the individual activities that make up a larger project.
Shows the order in which activities have to be undertaken.
Shows which activities can only taken place once other activities have been completed.
Shows which activities can be undertaken simultaneously, thereby reducing the overall time taken to complete the whole project.
Shows when certain resources will be needed – for example, a crane to be hired for a building site.
In order to construct a CPA, it is necessary to estimate the elapsed time for each activity – that is the time taken from commencement to completion.

Then the CPA is drawn up a based on dependencies such as:

The availability of labour and other resources
Lead times for delivery of materials and other services
Seasonal factors – such as dry weather required in a building project
Once the CPA is drawn up, it is possible to see the CRITICAL PATH itself – this is a route through the CPA, which has no spare time (called ‘FLOAT’ or ‘slack’) in any of the activities. In other words, if there is any delay to any of the activities on the critical path, the whole project will be delayed unless the firm makes other changes to bring the project back on track.

The total time along this critical path is also the minimum time in which the whole project can be completed.

Some branches on the CPA may have FLOAT, which means that there is some spare time available for these activities.

What can a business do if a project is delayed?

Firstly, the CPA is helpful because it shows the likely impact on the whole project if no action were taken.
Secondly, if there is float elsewhere, it might be possible to switch staff from another activity to help catch up on the delayed activity.
As a rule, most projects can be brought back on track by using extra labour – either by hiring additional people or overtime. Note, there will be usually be an extra cost. Alternative suppliers can usually be found – but again, it might cost more to get urgent help.
The key rules of a CPA
Nodes are numbered to identify each one and show the Earliest Start Time (EST) of the activities that immediately follow the node, and the Latest Finish Time (LFT) of the immediately preceding activities
The CPA must begin and end on one ‘node’ – see below
There must be no crossing activities in the CPA
East activity is labelled with its name eg ‘print brochure’, or it may be given a label, such as ‘D’, below.
The activities on the critical path are usually marked with a ‘//’
In the example below

The Node is number 3
The EST for the following activities is 14 days
The LFT for the preceding activities is 16 days
There is 2 days’ float in this case (difference between EST and LFT)
The activity that follows the node is labelled ‘D’ and will take 6 days



A simple example – baking a loaf of bread

Here is a simple example, in which some activities depend on others having been undertaken in order, whereas others can be done independently.

Activity
Preceded by
Elapsed time (minutes)

A weigh ingredients
-
1

B mix ingredients
A
3

C dough rising time
B
60

D prepare tins
-
1

E pre-heat oven
-
10

F knock back dough and place in tins
C&D
2

G 2 nd dough rising time
F
15

H cooking time
E & G
40





In this example, there is a clear sequence of events that have to happen in the right order. If any of the events on the critical path is delayed, then the bread will not be ready as soon. However, tasks D (prepare tins) and E (heat the oven) can be started at any time as long as they are done by the latest finish time in the following node.

So, we can see that the oven could be switched on as early as time 0, but we can work out that it could be switched on at any time before 71 – any later than this and it won’t be hot enough when the dough is ready for cooking. There is some ‘float’ available for tasks D and E as neither is on the critical path.

This is a fairly simple example, and we can see the LST and LFT are the same in each node. In a more complex CPA, this will not necessarily be the case, and if so, will indicate that there is some ‘float’ in at least one activity leading to the node. However, nodes on the critical path will always have the same EST and LFT.

Evaluation
CPA is a planning and project management tool. Whilst it can help ensure a project is completed as quickly as possible, and resources used as efficiently as possible, it does depend on the accuracy of the information used.

Just drawing up a CPA will not in itself ensure a project runs to plan; most projects encounter some delay or something unexpected, so managers need to use tool such as CPA to monitor the project and take swift action to rectify any problems.

These days, businesses use a software package such as Microsoft © Project ® to draw up and manage a CPA.

Examination technique
Some examination boards require A-level candidates to construct or complete a CPA during the examination. If you are lucky, you may just have to interpret one!

Many pupils find CPA quite difficult in practice, so the best way to help yourself is to do lots of examples so that you become familiar with the various options that might be presented to you.

Remember, even if you do get stuck, there are likely to be marks to be had by explaining what the CPA is for, by relating it to the case study, and describing any limitations to its usefulness. Remember, many projects can be brought back on track by use of extra money and labour.

It is beyond the scope of these revision notes to explain how to do draw one up from scratch – you need plenty of practice before your examination, so consult your teacher or use the exercises in your textbook.



Production & Operations Glossary - Key Terms
A B C D E F G H I J
K L M N O P Q R S T
U V W X Y Z





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Lean Production
Introduction
Cell Production
Just in time JIT
Kaizen, Quality Circles & Continuous Improvement
Time-based Management & Simultaneous Engineering
Production & Efficiency
Capacity Utilisation
Economies of Scale
Increasing and reducing productive capacity
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[Glenn]

Another example

www.netmba.com/operations/project/cpm/

[Glenn]

Another example

www-distance.syr.edu/edu5900cpa.html
Critical Path Analysis:

A Planning/Time Management Tool for Managing Research

By Roger Hiemstra

October, 2000



Abstract

This paper urges use of Critical Path Analysis (CPA) in formulating, scheduling, and managing the various milestones or activities involved in a research or any other type of project that requires advanced and careful planning. CPA involves the careful delineation and sequencing of such activities, determining the time necessary to complete them, and computing a critical path of activities around which the project must be managed for success. As a researcher or planner you are shown how to carry out each step in the CPA process through a series of visuals and corresponding narration. The calendar dating of a CPA network, utilization of Gantt charts, and other time management ideas are included.



What is Critical Path Analysis?

Critical Path Analysis can be defined as the logical sequencing of a series of events necessary for a successful research project in such a manner that the most efficient route to some culmination point can be calculated. Consequently, the critical path technique has a multitude of uses: (a) As an aid in time management, (b) as a provider of ongoing data for assessing progress, and (c) to give the researcher or program planner considerable information for decision-making.

CPA is a useful planning and management tool for several reasons:

A thorough identification of all major activities requiring time and resources must be made during the planning process.
Logical sequencing of these activities must be made.
The time required for each activity must be estimated or determined.
The overall research or planning project is scheduled according to the estimated times, resulting in a determination of the most efficient plan for carrying out the various activities.
Continuous evaluation of the planning and implementation progress according to a predetermined schedule is required so necessary decision-making for maintaining a schedule can be made.
Carrying out the above steps provides you with an empirically constructed schedule of research or planning activities to meet some self-imposed or institutionally required calendar of events. CPA also provides you with a visual picture through the development of a model network displaying how all research or planning functions tie together. The availability of computer software related to CPA techniques even means that information regarding progress in the planning and implementation process is available as often as you input related data.

How CPA is Utilized

Learning how to utilize CPA means understanding a few basic principles, procedures, and definitions. The terminology and process to be described in the following narration and visuals are somewhat unique to the CPA technique. Once these procedures are mastered, you will find them applicable to any type of planning or time management need.


Step One: List the Major Activities

The procedure begins by listing all the known or expected major activities to be undertaken in planning and managing a research or other type of project. The level of detail or finiteness of the activities will depend on your determination of their importance or "criticalness" to completing your project planning and management according to various time constraints. Over time in using CPA, whether by hand or by computer, you will "learn" how detailed you need to be for success in using the technique as a time management tool.

Listing the major activities requires a thorough analysis of the steps involved in initiating, implementing, and bringing to culmination a successful research or planning endeavor. Several activities are described below. The examples used relate to planning a conference or meeting to provide a common reference point for those not yet familiar with necessary research steps. It should be obvious there could be many variations or each activity could be divided into several smaller activities for the examples shown:

Formulating the meeting objectives
Selecting a meeting planning committee
Finalizing meeting site arrangements
Developing the meeting program
Advertizing/marketing the meeting
Obtaining meeting speakers
Making food and hotel arrangements
Arranging for displays and exhibits
Determining the meeting room needs
Establishing registration procedures
Finalizing the meeting program booklet
Finalizing meeting evaluation procedures
Managing the meeting logistics
Tabulating meeting evaluation results
Writing a final report

Step Two: Sequence the Major Activities

The next step is to sequence each activity into a logical order based on when it must or is most likely to occur. The sequence you select will be peculiar to your research or planning project, but certain activities logically precede others (for example, in planning some type of meeting formulating objectives almost always takes place before you obtain the meeting speakers). This step usually requires some reshuffling of activities before the final sequence is determined. Experience with planning and the CPA technique will facilitate this sequencing step.


Step Three: Construct an Activity Flow Diagram

In the third step you construct a schematic or flow diagram detailing the sequence of activities determined for an overall planning effort or research project. This step requires an understanding of three basic definitions:

Event - the start or completion point of a meeting task or activity. Events do not consume time or resources but are used as notations in constructing a CPA network.
Activity - the performance of an actual meeting task or activity. Activities do consume time and/or resources.
Network - the flow diagram constructed by connecting events; this details the sequence of activities for a particular meeting.
Figure 1 illustrates a simulated CPA network. It is important to reemphasize that events (typically represented by circles or squares in a network) do not consume time or resources, but merely are beginning or ending points of actual planning and management activities. They are usually identified by words within the circles or the circles are numbered and defined elsewhere. Activities are the arrows connecting various events. They are typically represented by capital letters shown on or near the arrows. Each activity can be defined in a footnote to the network or on a separate page if necessary for clarity's sake or if the network is to be part of a formal meeting or research plan (e.g., activity "A" could be defined as formulating the meeting objectives). Arrows made up of dashes or arrows identified with the word "Dummy" represent dummy activities, those activities requiring no time or resources.



Arrowheads indicate the flow direction (e.g., "finalizing the meeting site arrangements" must take place before "advertizing and marketing the meeting"). More than one arrow leading to or from an event indicates that more than one activity is occurring at the same time. In addition, it should be noted that the length of an arrow has no relationship to the amount of time; arrows merely serve as connectors between events and show the direction of the flow. See the following footnote for explanatory information on a short cut method of displaying activity paths by "assuming away" dummy activity arrows.



--------------------------------------------------------------------------------





--------------------------------------------------------------------------------


Step Four: Estimating the Time for an Activity

The next step involves estimating the time required to perform each activity. Time is usually represented on most networks in days or in weeks. In the CPA process it is recommended you estimate the time required for each activity utilizing as guides such criteria as experience, suggested time requirements made by colleagues or planning authorities, and known limitations of staff, resources, and money. A thoroughly constructed network might even have defined how many people and who will be working on a given calendar day, although there will be occasions when approximations will be just as useful.

Figure 2 displays the previously constructed network with time estimates included. They typically are displayed as numbers on an activity arrow. The time estimates are simulated for this example and they will always be specific to any single planning project, although similarities will occur from project to project. They are used here primarily to facilitate an explanation of the CPA technique.




The simulated network utilizes 8-hour working days and a seven day week, assuming that weekends and overtime costs need to be computed if a dollar figure is attached to the network and any corresponding time requirements of salaried personnel are considered in overall management of whatever project being considered. In addition, concurrent activities will require consideration of time needs in relation to the availability of total staff and resources.


Step Five: Computing the Expected Times to Complete All Activities

Following an estimation or determination of the time required for each activity, the planner needs to calculate totals or the earliest possible time that each event can be reached. Symbolized on Figure 3 by the letter "T," this total is derived by summing the estimated times of all activity paths leading to any particular event.

As Figure 3 shows, times have been calculated for all events in the example. They are shown at the top of the corresponding event.




Step Six: Determining the Critical Path

A critical path, or that path of activities that must be completed within the times shown if the entire plan is to stay on schedule, can now be determined. Symbolized on the network by small perpendicular lines or hash marks, the critical path is found by selecting those activity paths requiring the most time to arrive at any one event. In other words, to arrive at the "Conference Room Needs Determined" event from the "Conference Site Finalized" event, it requires more time to complete activity D (see Figure 1), then activity G, and then activity I, than to complete either of the other two paths. More discussion of the critical path and its usefulness is in a later section.

Two concepts must be understood before this step can be achieved successfully. First dummy activities (represented on the network simulated in this paper as lines that contain dashes) to not consume time. They merely are logical connectors between two events. In other words, the meeting planner cannot declare the overall meeting completed until the final report is written, but immediately upon that task the meeting can be declared as completed. As a further illustration, a dummy arrow might have been drawn from the "Meeting Site Finalized" event to the "Meeting Program Developed" event. In this case, that event would not take place until all activities related to both formulating objectives and finalizing the meeting site had been completed. Thus, when summing up times to a certain event, the dummy activity times are assumed to be zero.

Secondly, time totals up to any event are based on the earliest possible time that event can be reached. Thus, as all activities leading to an event (more than one arrow) must be completed before it is considered reached, the activity path actually taking the most amount of time to an event is determined by adding all activities on the critical path. For example, as shown in Figure 3 finalizing the meeting site, developing the meeting program, arranging for food and hotel, determining the meeting room needs, finalizing the meeting booklet, managing the logistics, tabulating the evaluation results, and writing the final report represent the longest path, the earliest possible time, and the critical path. No other activity paths would take longer; thus the "conference completed" event is reached in the earliest possible time of 60 weeks.


Step Seven: Constructing a Gantt Chart

Once all of the totals have been reached, the planner can make the first application of the CPA process. Simply by starting at the first event with some selected or mandatory calendar date, completion dates at each even based on the corresponding totals can be established. Figure 4 shows the simulated network with appropriate calendar dates superimposed based on a July 1 starting date. A critical path also is superimposed (represented on the network by double arrows) to provide you with a visible reminder of what is required to keep on schedule (as will Gantt charts--see Figure 5).




It also has been the experience of many planners that a corresponding "Gantt" chart (see Figure 5) can be useful in quickly and constantly assessing a project's progress. (Henry Gantt, a management pioneer, introduced the bar graph concept many years ago. It is simply another way of displaying graphically the activities that comprise a planning or research project.) This bar graph approach reveals how many activities are taking place at once, when one activity must begin in relation to another, and how long various activities are in progress. In essence, you take each activity on the network, stretch the length to the appropriate calendar length, and place it on the graph. You can even color code the critical path as a quick visual reminder of what is crucial for staying on time. Appropriate decisions to add resources or to have staff members work on other activities can be made from these types of information if certain activities crucial to keeping on schedule begin taking longer than expected. Most computerized programs are capable of making Gantt charts.




CPA and Decision-Making

The ability to make appropriate planning and managing decisions based on the CPA process, in addition to its scheduling usefulness, can be enhanced by adding two final steps to the process. These steps are crucial if you find that the initially constructed network requires more days or weeks than you had originally estimated or if the final completion date must be moved up for some reason. Information is available that allows you to make the most sound decisions regarding where to apply additional resources in order to meet such needs.

The first of these additional steps begins by establishing what is that final finishing date or allowable completion time. In Figure 6 it has been assumed that 60 weeks is an acceptable time frame and that it will allow you to run the meeting as scheduled. Then "L" (latest allowable time) is set equal to 60 weeks at the "meeting completed" event. On the network all "L" times are shown at the bottom of the corresponding event (Figure 7 converts these to slack times)




To calculate the "L" times for all events on the network, you must work backwards starting from the "meeting completed" event, subtracting the appropriate activity times. For example, as the meeting completion activity (closing accounts, storing evaluation data, writing the final report, etc.) was approximated to require three weeks, the latest allowable time at the "evaluation results tabulated" activity is 57 weeks. This process is repeated throughout the network.

It needs to be emphasized that when more than one activity path leads backward from an event, the activity path requiring the most time to complete is the one whose time is subtracted from the "L" time up to that point. This is demonstrated on the network, for example, in calculating the latest allowable time for the "food and hotel arrangements made" event. Although the smallest "L" times are the dummy activity from "meeting program booklets finalized" back to "displays and exhibits arranged" and activity H, it will require considerably more time to complete activities K and I, the activities leading backwards from "meeting program booklets finalized" through "conference room needs determined" to "food and hotel arrangements made." The corresponding subtractions (54 - 0 - 8 = 46 -vs- 54 - 4 - 10 = 40) show that the smallest "L" time is equal to 40. Following this procedure the appropriate "L" times at each even can be calculated.

The next and final step begins by determining a "slack" time at each event. Slack time is defined as the amount of excess time available to reach any particular event. Another way of looking at this is that slack is the number of weeks the latest allowable time (L) exceeds the earliest possible time (T) an event can be reached. It is determined by subtracting the "T" time from the "L" time at each event. Figure 7 details the network with all the slack (S) times shown above the corresponding event. This should not be confused with the various "T" times previously displayed above the corresponding events in Figure 3. If you were to have all the various times calculated via a computerized program, the results typically are displayed in columns under appropriate headings rather than superimposing them all on a single, and therefore most likely, congested looking network.




In explanation of the slack times, a value greater than zero indicates that there are that many weeks of spare time in terms of completing that event. The "slack" time concept also can be used advantageously when the required completion or contract time is equivalent to that determined in the original calculations. Those events with the least amount of slack (usually zero if the "L" times and "T" times are set as equivalent to each other--there are times when the number could be minus if the "L" time was required by law or some other reason to be set at a certain date and that date was prior to the calculated "T" time) will always lie on the critical path, thus facilitating the path's determination.

In addition, by setting the final event's "L" time equal to the final "T" time and computing all the slack times, the planner can identify those events where excess amounts of slack time exist. Thus, if at any point the overall plan falls behind schedule, the planner can divert staff time from activities not on the critical path to those more critical activities and often thereby restore the plan to its original schedule. Thus, in the simulated example if the overall project fell behind schedule before the meeting room needs had been determined, those people working on such activities as marketing and advertising or obtaining the meeting speakers could be asked to pitch in for awhile on something like developing the meeting program or making food and hotel arrangements.

Of course, once any event either is reached early or late, the remaining network must be recalculated with new calendar dates. For example completing any one of the activities on the critical path might be shortened by one or more weeks by such actions as asking people to work overtime, jobbing something out to another organization, or hiring temporary people. Note, too, that the critical path always passes through those events showing the least amount of slack, although there sometimes can be more than one critical path when the slack times are equivalent on two different paths leading to a certain event or the final completion event.

This type of information should aid you in making a variety of decisions. If the research or planning project is faced in the beginning with negative slack on the critical path because of some forced contractual obligation (such as a college requiring the completion of a thesis by a certain date in order to graduate), then you will know immediately that some changes will be required in order to meet the required schedule. You also will know where the most critical of these changes are needed. Available staff or resources from those events with surplus slack time might be shifted to more critical activities, new resources or staff assistance may be required to speed up certain activities, or you may need to decide to eliminate or greatly reduce certain activities.

The CPA procedure should facilitate most planning and research projects. It forces you as planner to organize and sequence the required activities carefully. Information also is provided that will enable a calendar of meeting events to be constructed. The Gantt chart, especially if reproduced in a very large format or displayed electronically for those used to computer networks, can serve as a major discussion point at staff meeting for determining progress or staff assignments. Finally, for the individual research or meeting planner the CPA network or Gantt chart can serve as a daily planner or self-disciplining tool to facilitate day to day meeting management actions.

[Glenn]

Another sourse see link to connect to various paths mentioned.

en.wikipedia.org/wiki/Critical_path

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Critical Path may refer to:

Critical path method, an algorithm for scheduling of activities
Critical Path (book) by Buckminster Fuller
Critical Path (video game), an interactive movie computer game