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Microsoft Project 2010 : Refining a Project Schedule (part 9) - Paying More for Faster Delivery

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1/13/2015 3:00:05 AM

Modifying Task Dependencies to Overlap Tasks

Fast-tracking means starting the next task before its predecessor is complete. For instance, you could tell your accountants to start counting the chickens before all the eggs have hatched. When you identify partial overlaps, you create them in Project by adding negative lag to the link between the tasks.

When the link lines in your project look like fishing line in a tackle box, finding the right link line in the timescale is impossible, so don’t even try. The Task Information dialog box is the easiest place to add lag.

Here are the steps:

  1. In the Gantt Chart table area, double-click the successor task.

    The Task Information dialog box opens.

  2. Select the Predecessors tab.

    All the predecessor tasks appear in the list, even those that aren’t on the critical path.

  3. Click the Lag cell for the predecessor you want to overlap, and then type a negative number for the overlap .

    For example, to overlap the two tasks by 2 days, type -2d. You can also overlap by a percentage of the predecessor task’s duration. For instance, if you type -25% on a predecessor that takes 8 days, the overlap is 2 days. Keep in mind that a percentage lag changes the length of the overlap when the predecessor duration changes.

  4. Click OK.

    The value appears in the Lag cell, and the task bars overlap in the timescale.

Paying More for Faster Delivery

Spending more money to deliver in less time can make financial sense. A high-tech doodad that will be obsolete in 2 years can’t afford a delay getting to market. The sales you make could add up to more than the premium you have to pay to finish the project earlier.

Crashing is the term project managers use for shortening a schedule by throwing more resources at tasks. It’s not as dire as it sounds, although it sometimes describes what happens when a horde of people try to work on the same task. To the uninitiated, crashing seems like an easy choice. If two people can build your website in 12 weeks, then four web developers should wrap it up in only 6 weeks, but it doesn’t always work out that way. 

It’s easy to assume that crashing won’t change cost—it looks like you’re paying the same rate for the same number of hours. In reality, there’s always a trade-off between time and money. When you crash tasks, you must choose the tasks that shorten the schedule for the least amount of money. That’s because every task has a magical duration that results in the minimum cost. If the task runs longer, you spend more money on things like office space, people’s salaries and benefits, and keeping the freezer stocked with Cherry Garcia ice cream. Ironically, shorter tasks can cost more, too—for items like additional computers, higher-cost contractors, and managing the larger team it takes to expedite the work.

Time vs. Money

Stakeholders might open the checkbook to crash a project, but they don’t want to spend more than they have to. Shortening tasks that aren’t on the critical path is a waste of money, because the project duration doesn’t change a bit. At the same time, crashing doesn’t mean shortening every task on the critical path. Like cars, some tasks cost more to crash than others. Your job is to shorten the schedule for the least amount of money.

Crash tables help you compare the cost and time you can save by crashing different tasks. For example, one task might cost an additional $50,000 to cut 2 weeks from the schedule, whereas another task cuts 2 weeks for only $25,000. To choose cost-effective tasks, you must compare apples to apples, that is, how much it costs for each week of duration you eliminate. One method is to build a crash table in an Excel spreadsheet. You can enter the duration you can cut and the cost, and create an Excel formula that calculates the cost per week (or month or day). The next section explains how to do that.

Long critical tasks are the best candidates for crashing, since you can eliminate longer durations in fewer tasks. Shortening a few long tasks may cost less—and save more time—than crashing a bunch of shorter tasks.

Reality Check: When Crashing Doesn’t Work

Sometimes, crashing simply won’t work. Some tasks can’t finish in less time, no matter how many resources you assign (much to the dismay of most pregnant women).

In many cases, adding more resources increases duration instead of decreasing it. New people need time to get up to speed, so they run up the cost while they’re less productive than the original team. The problem can be compounded because the original resources sacrifice productivity when they have to help the new people. And more bodies mean more costs for supervision and communication. To learn more, read The Mythical Man-Month (Addison-Wesley, 1995) by Frederick Brooks.

Using a Spreadsheet to Choose Tasks to Crash

You could create custom fields in Project that hold crash costs and durations, and calculate the crash cost per week with formulas you define for the custom fields. However, it’s faster to move task data to an Excel spreadsheet and calculate crash costs there.

Finding the perfect combination of tasks to crash can get complicated. One task might offer several weeks worth of low-cost crashing. However, if shortening that task by 2 weeks takes it off the critical path, there’s no point spending money to shorten it any more. The most effective approach is to crash one task at a time (by adding resources to it in Project), and then evaluate the critical path again to see what the next step should be.

Since you start with the longest tasks and usually crash only a few, start by sorting the critical tasks by duration, and then copy the first several tasks from Project to Excel. Here are the steps for finding critical tasks to crash, and then copying them to Excel:

  1. With a task-oriented view displayed, click the down arrow to the right of the Task Name column heading, and then choose Filters→Critical .

    To hide summary tasks, choose Format→Hide/Show, and then turn off the Summary Tasks checkbox.

  2. To list the longest critical tasks first, click the down arrow to the right of the Duration column heading, and then choose Sort Largest to Smallest.

    The task IDs and task bars show up out of order, but the longest tasks appear at the top of the task list. In addition to copying task names to Excel, Duration and Cost come in handy if you want to sort tasks in Excel by their original duration or cost.

    Tip

    The Entry table places the Task Name and Duration columns one after the other. To simplify copying the fields you want, insert the Cost field immediately after Duration. Right-click the Start column heading, and then choose Insert Column. In the field name drop-down list, choose Cost.

  3. Drag from the Task Name cell of the first critical task to the Cost cell for the last critical task you want to copy, and then press Ctrl+C.

    Project copies the cells to the Clipboard.

  4. In Excel, click the top-left cell where you want to copy the values, and then press Ctrl+V.

    Excel pastes the values into worksheet cells starting at the top-left cell and filling in cells to the right and down, as illustrated in Figure 13. (If the values aren’t completely visible, widen the columns by dragging the dividers between the column headings.)

    Project durations include time periods (days, weeks, and so on). If all the units are the same, use Excel’s Replace command to remove the units and leave the numbers: Press Ctrl+H and type the unit in the “Find what” box. Leave the “Replace with” box empty, and then click Replace All. If tasks use different time periods, manually convert each duration to the corresponding number of weeks.

    Figure 13. Project durations include time periods (days, weeks, and so on). If all the units are the same, use Excel’s Replace command to remove the units and leave the numbers: Press Ctrl+H and type the unit in the “Find what” box. Leave the “Replace with” box empty, and then click Replace All. If tasks use different time periods, manually convert each duration to the corresponding number of weeks.

  5. In the first three blank columns to the right of the copied values, add headings for crash reduction, crash cost, and crash cost per week .

    Fill in each row with the total amount of time you can shorten the task, and how much it costs to do so.

  6. In the first blank crash cost per week cell, type the formula to divide the crash duration by the crash cost (for instance, = D2/E2).

    You can then drag the copy handle over all the other crash cost per week cells so Excel can calculate the values.

  7. To find the least expensive tasks to crash, sort the rows first by the amount of schedule reduction and then by the crash cost per week.

    In Excel, Choose Data→Sort. In the Sort dialog box, in the “Sort by” drop-down list, choose Crash Reduction or the column name you entered. In the Order drop-down list, choose Largest to Smallest. Click Add Level to add a second sort criterion. In the “Then by” drop-down list, choose Cost Per Week or the column name you entered. This time, in the Order drop-down list, choose Smallest to Largest. Click OK. The tasks appear with the longest reductions in duration first and the smallest cost per week to the largest, as shown in Figure 13.

  8. Switch to Project and add resources to a task to shorten its duration.

    Review the critical path to see whether the results are what you want. For example, if the task is no longer on the critical path, you may want to scale back on how much you crash it.

    Repeat this step until the project duration is the length you want—or the cost prohibits shortening it any further. At that point, you may need to reduce the project scope.

 
Others
 
- Microsoft Project 2010 : Refining a Project Schedule (part 8) - Overlapping Tasks - Finding Tasks to Fast-Track
- Microsoft Project 2010 : Refining a Project Schedule (part 7) - Adjusting Resource Assignments - Assigning a Different Resource , Using Slack Time to Shorten the Schedule
- Microsoft Project 2010 : Refining a Project Schedule (part 6) - Adjusting Resource Assignments - Increasing Units to Decrease Duration
- Microsoft Project 2010 : Refining a Project Schedule (part 5) - Project Tools for Change - Undoing Changes
- Microsoft Project 2010 : Refining a Project Schedule (part 4) - Project Tools for Change - Seeing What Changes Do
- Microsoft Project 2010 : Refining a Project Schedule (part 3) - Evaluating the Project Schedule - Reviewing Project Costs
- Microsoft Project 2010 : Refining a Project Schedule (part 2) - Evaluating the Project Schedule - Finding the Best Tasks to Shorten
- Microsoft Project 2010 : Refining a Project Schedule (part 1) - Evaluating the Project Schedule - Comparing Finish Dates to Deadlines
- Microsoft Onenote 2010 : Using Tables to Organize Information (part 5) - Deleting a Row in a Table, Using Keyboard Shortcuts to Modify Tables
- Microsoft Onenote 2010 : Using Tables to Organize Information (part 4) - Selecting a Row in a Table,Selecting a Single Cell in a Table
 
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