Time Management

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Answers to the following questions can be found in Chapter 2, ''Time Management," unless otherwise noted.

Note that activities in a calendar schedule start on the beginning of the time period that they start on and end at the end of the time period that they finish on. A two-day activity starts on May 5 and ends on May 6, ES and EF.

The free float or slack is the amount of time that an activity can be delayed before it affects the schedule of any other activity. Activity F has free float but activity D does not. Both have seven days of float, total float, or plain old float. When calculating schedules and float with leads and lags, it is best to look at the next activity with no lead or lag and, after determining the dates, change them by the amount of the lead or lag.

The free float or slack is the amount of time that an activity can be delayed before it affects the schedule of any other activity. Activity F has free float but activity D does not. Both have seven days of float, total float, or plain old float.

Critical path is the list of activities that have zero total float. It is dangerous to find the path that has the longest sum of the durations. Path A B D F H has a duration of eight days but has a sum of the durations of ten days.

The late start for activity F is May 12. It has a late start that is calculated to be two days before the late finish of activity D. With leads and lags it is best to calculate the LS of the dependent activity, then the LF of the independent activity, and then adjust the LF of the independent activity to consider the FS lead.

The first work of the project is done on May 1, and the last work of the project is finished on May 20.

There is a lead of two days associated with the finish-start relationship between activities D and F. If the relationship were a normal FS relationship, the ES of activity F would be May 7. A two-day lead means it will start two days earlier, or May 5.

Since activity F has seven days of float it can be delayed for as much as seven days before it has any effect on the project completion.

The early finish date of activity A is the same as its start date and the start of the project. Activities start on the beginning of the time period that work begins and end on the end of the time period that work finishes. This activity takes one day beginning in the morning of May 1 and finishing in the afternoon of May 1.

The figure is called a precedence diagram. It is recognizable because boxes are used to indicate the activities. The arrows in a precedence diagram indicate the logical relationship between the activities. The information about the activity is inside or around the box. An activity on arrow diagram will use circles to indicate events and the activity information will be put on the arrows. The Gantt chart has no logic shown normally (now available on some project management software). The length of the Gantt bar is proportional to a time scale showing the duration of the activity. Although this diagram is also a network diagram, there are many other network diagrams in the world. Precedence diagram is a much better answer.

The finish-finish relationship in a precedence diagram says that the independent activity must finish before the dependent activity is permitted to finish. In the schedule, if the turkey took five hours to roast and the sweet potatoes took one hour, the turkey would be scheduled to start at 1:00 p.m. and the sweet potatoes would be scheduled to start at 5:00 p.m. Both would finish at 6:00 p.m.

The following table refers to questions 12 through 15.

o

p

ml

EV

SD

CP EV

CP SD

CP VAR

A

1

1

1

1

0

1

0

0

B

2

B

B

2.sBBBBB

0.166667

C

10

1B

12

11.83333

0.5

11.83333

0.5

0.25

D

5

5

5

5

0

E

B

6

4

4.166667

0.5

4.166667

0.5

0.25

F

1

1

1

1

0

G

5

s

6

6.166667

0.5

H

9

1B

10

10.33333

0.666667

10.33333

0.666667

0.444444

I

5

5

5

5

0

5

0

47.33333

Total

32.33333

Total Sqrt of Total

0.944444 0.971825

33.30516 34.27698 35.24881

31.36151 30.38968 29.41786

The expected value of the project is the expected value of each of the tasks that are on the critical path, A C E H I. The approximate expected value is the sum of each of these task's optimistic, pessimistic, and four times the most likely estimate divided by 6. When calculating the length of time that the project takes, it is important that you remember to include only the critical path activities. Other activities in the schedule are done in parallel with the critical path activities.

The 95% probability of the estimate is the expected value ± 2 standard deviations of the total standard deviation of the critical path items. To total the standard deviation, first square the value for each critical path item's standard deviation, add them up, and take the square root of the total.

The expected value for activity B is the sum of the optimistic, pessimistic, and four times the most likely value, all divided by 6.

The standard deviation for activity B is the difference between the optimistic estimate and the pessimistic estimate divided by 6.

Fast tracking a schedule is finding activities that can be done in parallel that were originally scheduled to be done in sequence.

Crashing a schedule is improving the project completion date by any means that is economical and feasible. In crashing a schedule an effort is made to find the largest schedule reduction for the least additional cost.

The baseline schedule as well as the baseline budget and the baseline scope are the original project plans plus or minus any approved changes. There are many other terms used to describe schedules, but the definition given is the definition of the baseline schedule and therefore the best answer.

Bar charts, also called Gantt charts, show activity start and end dates as well as expected durations, but do not usually show dependencies. They are relatively easy to read and are frequently used in management presentations. In a Gantt chart there is a horizontal time scale. Activities are represented as bars above the time scale in such a way that the length of the bar is proportional to the elapsed time of the activity. The start of the activity is on the left side of the bar and is above the date that it starts. The right-hand side of the bar is located over the finish of the activity.

The critical path activities are those activities that have zero float. There are exceptions. When activities are forced to be done on specific dates (date constraints), it is possible to create negative float. When the project is resource constrained the critical path may change due to resource constraints.

Resource leveling is a tool in most project management software and can also be done manually. In resource leveling an attempt is made to reduce overutilization of resources to their normal utilization.

At the end of two weeks this task is 75% complete. The PV was to be 4 person-weeks, two people working full time for two weeks. The EV is therefore 3 person-weeks, .75 X 4. The AC is 2 person-weeks. The cost performance index is the EV / AC. CPI = 3 person-weeks / 2 person-weeks = 1.5.

Although total float is assigned to each of the tasks in the sequence, the total float can be used by any of them and it can be used only one time by any of them. If the tasks are ABC D E and each has one day of float, if A is delayed by one day, the total float at B C D E reduces to zero.

Monte Carlo analysis is a simulation technique that assigns durations to tasks in a schedule and then calculates the schedule information. It repeats this assignment and calculation many times and then reports statistical results, including the percent of time a task is on the critical path.

Precedence diagramming method (PDM). This is a method of constructing a project network diagram using nodes to represent the activities and connecting them with arrows that show the dependencies. This technique is also called activity-on-node (AON) and is the method used by nearly all project management software packages.

Arrow diagramming method (ADM). This is a method of constructing a project network diagram using arrows to represent the activities and connecting them at nodes to show the dependencies. This technique is also called activity-on-arrow (AOA) and, although less prevalent than PDM, is still the technique of choice in some application areas.

The project schedule includes at least planned start and expected finish dates for each detail activity. A schedule update is any modification to the schedule information that is used to manage the project. Float is the amount of time that an activity may be delayed from its start without delaying the project finish date. Although the project's budget is the time phased expenditure of the project funds, it is not the project schedule and therefore the best answer.

Mandatory dependencies are those which are inherent in the nature of the work being done. Discretionary dependencies are those which are defined by the project management team. They should be used with care (and fully documented) since they may limit later scheduling options.

Resource requirements. The resources assigned to them will significantly influence the duration of most activities and the project itself.

Resource capabilities. The duration of most activities will be significantly influenced by the capabilities of the humans and material resources assigned to them.

Critical path method (CPM) calculates a single, deterministic early and late start and finish date for each activity based on specified, sequential network logic and a single duration estimate. Program evaluation and review technique (PERT) uses sequential network logic and a weighted average duration estimate to calculate project duration. Although there are surface differences, PERT differs from CPM primarily in that it uses the distribution's mean (expected value) instead of the most likely estimate originally used in CPM and associates the standard deviation of the estimate to allow the range of values and a probability of occurrence to be calculated for the project.

The activity that has eighteen days of free float can be rescheduled without having to reschedule any other activity in the project. If this activity is rescheduled to start two weeks later, the resource will not be overutilized, and the project will remain on schedule.

The person who is working on the task that has free float of five days can be used on the task that is in trouble for five days without affecting the other task schedules in the project. The person working on the task that has total float of eight days can be used on the task that is in trouble, but since there is zero free float for this task, there will have to be a rescheduling of other tasks to allow this.

The logical analysis of the schedule often produces a preliminary schedule that requires more resources during certain time periods than are available, or requires changes in resource levels that are not manageable. Heuristics such as ''allocate scarce resources to critical path activities first'' can be applied to develop a schedule that reflects such constraints. Resource leveling, because of the limited availability of the resources, often results in a project duration that is longer than the preliminary schedule.

The Guide to the PMBOK defines the lowest level of the work breakdown structure as the work package. It goes on to say that the work package is a unit of work that can be assigned to a person or organization. It also says that the work package can be broken down into tasks, and that tasks can be broken down into activities.

When a risk is identified, budget and schedule time are identified and put into the contingency reserve. If the risk actually occurs the money is used from the contingency reserve and added to the operating budget of the project. The total project budget contains the operating project budget or baseline, contingency reserve, and the management reserve. The project budget baseline is increased by the amount of the risk although the total project budget stays the same. The schedule baseline is changed to reflect the new activities that have to be done.

The Guide to the PMBOK gives the following as inputs to the activity definition:

• Work breakdown structure

• Scope statement

• Historical information

• Constraints

• Assumptions

Fast tracking a project means that project tasks and activities are rescheduled from being done in sequence to being done in parallel. Crashing a project means doing anything practical that can be done to reduce the schedule. Fast tracking involves only doing things in parallel that would have otherwise been done in sequence.

The CPM or critical path method is used to determine the activities that have zero float or close to zero float. These activities should be managed more carefully than other activities in the schedule since other activities not on the critical path will have free float and total float that allows their schedules to be more flexible.

PERT stands for program evaluation and review technique. In PERT each of the activities has the optimistic, pessimistic, and most likely duration estimated. A weighted average is then taken to estimate the expected value of the activity. The weighted average is calculated by adding the optimistic, pessimistic, and four times the most likely duration and dividing by 6. The standard deviation of the activity can also be calculated by subtracting the optimistic duration from the pessimistic duration and dividing by 6.

In the PERT calculation the standard deviation is calculated by squaring the standard deviation for each of the activities on the critical path of the project, adding them together, and then taking the square root. This is the standard deviation of the project. Plus or minus two standard deviations from the expected value of the project duration will have a range of values such that the project has a 95% probability of actually finishing within the dates calculated.

PERT is a probabilistic method used to determine the estimated project completion based on the statistical estimating of the project durations. CPM is a deterministic method using specific values for activity and task durations.

The Guide to the PMBOK defines the lowest level of the work breakdown structure as the work package. It goes on to say that the work package is a unit of work that can be assigned to a person or organization. The work package can be broken down into tasks, and tasks can be broken down into activities.

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