Workshop 8 - Scheduling Calculations

Background

We want to look at the Network Diagram and practice calculating Early and Late dates with a simple manual exercise.

Assignment

1. Apply the Network Diagram view by right clicking in the dark band on the left hand side of the screen and selecting it.

2. Hide the Summary tasks by selecting Format, Show/Hide group, Summary Tasks.

3. Use the buttons to zoom in and out.

4. Right-click in the Network Diagram, select Layout to open the Layout form and select Allow manual box positioning.

5. You should now be able to reposition the boxes manually by left-clicking and dragging.

6. Reapply the Gantt Chart View.

7. Calculate the Early Dates, Late Dates, and Total Float for the following activities, assuming a Monday-to-Friday working week and the first activity starting on 01 Apr 19.

8. See over the page for the answer:

Answer to Workshop 8

Forward Pass EF = ES + DUR –1

Backward Pass LS = LF – DUR +1

Float Calculation TF = LS – ES

9. The Early Bar is the upper bar, the Late Bar the lower bar and the end of the Total Float bar, which is the thin bar, ends at the Late Finish date.

11 CONSTRAINTS

Constraints are used to impose logic on tasks that may not be realistically

scheduled with logic links. Microsoft Project will only allow one constraint against a given task with the exception of a Deadline Date. This chapter will deal with the following constraints in detail, which are the minimum number of constraints that are required to effectively schedule a project:

• Start No Earlier Than

• Finish No Later Than

These two constraints may be applied to summary and detail tasks; all others may only be applied to detail tasks.

• Start No Earlier Than (also known as an “Early Start” constraint) is used when the start date of a task has been set by a client or an external event. Microsoft Project will not schedule the task early start date prior to this date.

• Finish No Later Than (also known as a “Late Finish” constraint) is used when the latest finish date is stipulated. Microsoft Project will not show the task’s Late Finish date after this date, but the Early Finish date will be able to exceed this date and Negative Float will be generated when the Late Date is earlier than the Early Date. This represents the amount of time to be “caught up” to finish the project on time.

The following chart summarizes the methods used to assign Constraints to Tasks:

Topic Notes for Creating a Constraint

• Open the Task Information form.

Double-click on the task and select the Advanced tab.

• Display the Constraint Type and

Constraint Date columns.

Apply the Constraint Table or insert the columns in an existing table.

• Type a date into a task Start or Finish date field of the Task Information form or the Details form or a column.

A date typed in a task Start field will apply a Start No Earlier Than constraint of that date, without warning. A date typed in a task Finish field will apply a Finish No Later Than constraint, without warning.

• Display a Combination

Open the bottom pane by right-clicking in the Gantt Chart and selecting Show Split,

view displaying the Task Details form in the

bottom pane.

Right-click on the vertical band on the bottom left-hand side of the screen labeled Task Form and select from the menu Task Details form.

There is an option found under the File, Options, Schedule tab, Scheduling options for this project: section, titled Tasks will always honor their

constraint dates. This function is described in detail in the OPTIONS chapter, Schedule section. When this option is checked, which is the default, constraints override a logic link. When unchecked, a logic link will override a constraint and a task may be delayed.

Tasks will always honor their constraint dates should never be checked.

Only one constraint may be applied to a task or milestone except when a Deadline Date is assigned. Oracle Primavera products allow two

constraints per task and Asta Powerproject has a Schedule Between constraint which is effectively assigning two constraints to a task.

A full list of constraints available in Microsoft Project is:

• As Soon As Possible

This is the default for a new task. A task is scheduled to occur as soon as possible and does not have a Constraint Date.

• As Late As Possible

A task will be scheduled to occur as late as possible and does not have any particular

Constraint Date. The Early and Late dates have the same date. A task with this constraint has no Total Float and will delay the start of all the

successor tasks that have Total Float.

• Start No Earlier Than This constraint sets a date before which the task will not start.

• Start No Later Than This constraint sets a date after which the task will not start.

• Must Start On

This constraint sets a date on which the task will start. Therefore the task has no float. The early start and the late start dates are set to be the

same as the Constraint Date.

• Must Finish On

This constraint sets a date on which the task will finish. Therefore has no float. The early finish and the late finish dates are set to be the same as the Constraint Date.

• Finish No Earlier Than This sets a date before which the task will not finish.

• Finish No Later Than This sets a date after which the task will not finish.

• Deadline Date

This is similar to applying a Finish No Later Than constraint. This offers the opportunity of putting a second constraint on a task.

The author recommends that constraints should be used as sparingly as possible and only used to represent events that may not be reasonably represented with relationships. These would often be events outside the control of the project manager such as the date a client will release a site to commence work or a predetermined time a project must be complete by.

Earlier Than constraints operate on the Early Dates and Later Than constraints operate on Late Dates. The picture below demonstrates how constraints calculate Total Float (Total Slack) of tasks (without predecessors or successors) against the first task of 10 days’ duration:

1. An Expected Finish is used in Oracle Primavera software to

calculate the remaining duration of a task. There is no equivalent of this constraint in Microsoft Project.

2. A task assigned with an As Late as Possible constraint in Oracle Primavera software will schedule the task so it absorbs only Free Float and will not delay the start of successor tasks. In Microsoft Project, a task assigned with an As Late as Possible constraint will

be delayed to absorb the Total Float and delay all its successor tasks, not just the task with the constraint. Therefore an As Late as Possible constraint should be used with care in Microsoft Project.

3. The Must Start On and Must Finish On are hard constraints and will not allow Float to calculate through the constraint dates and will effectively cut the schedule into two.