The project manager controls the project value stream. During execution, the project managers' primary question is, when should I take action to recover buffer? The
project manager also must ensure smooth handoffs between the task managers to maintain flow and aid the project team in communication and problem solving. The project manager also controls project changes.
In addition to buffer-report-driven decisions, project managers also address how to deliver technical quality on time and for or under the estimated cost. Project-level operational decisions include the following:
• Disposition of material that is not up to specifications (this includes, for R&D projects, not getting the hoped-for result);
• Requests for additional time or money to complete activities;
• Requests to add scope (some day, some project may even have a request to reduce scope!);
• Unanticipated resource conflicts;
• Late activities that may threaten the delivery date;
• Unanticipated external influences (e.g., accidents, weather, new regulations) and unfulfilled assumptions (e.g., soil conditions dictate a need to put in pilings before construction);
• Recovery from mistakes.
Project managers should monitor the project buffer and each feeding buffer at the appropriate time intervals for the project, usually daily but at least weekly. For buffer management to be fully useful, the buffer monitoring time must be at least as frequent as the shortest task duration. If the buffers are negative (i.e., the latest activity on the chain is early relative to the schedule date) or less than the red bufferpenetration criteria, the project manager should not act on the project. If the buffer penetrates between the yellow and red thresholds, the project manager should watch closely and plan actions (create buffer-recovery plans; see Section 8.5) for the buffer-penetrating chains to accelerate the current or future tasks and recover the buffer. If the buffer penetrates by more than the red criteria, the project manager should implement the planned buffer-recovery action. This process provides a unique, anticipatory project-management tool with clear decision criteria.
Note that managing the feeding buffers helps protect the overall schedule from delays in merging paths, including paths that merge at the project buffer. Action criterion for the feeding buffers can be the same as for the project buffer, although frequently feeding buffers penetrate very rapidly, or not at all.
Buffer reporting relies on realistic estimates of how many days are left to complete on a task, or RDU. There is often a tendency to report a project as "on schedule" until the due date arrives. With the critical-chain measurement system, that amounts to subtracting the days worked on the task from the total duration estimate. Project managers should question estimates that are repeatedly on schedule. A useful aid to estimating is to ask people, particularly on the critical chain or on feeding chains with significant buffer penetration, to explain the basis for their RDU estimate.
Project managers should use plotted trends of buffer utilization. This provides a measure and trend of the rate of buffer consumption by plotting the amount of buffer consumed versus the amount of critical chain accomplished as illustrated by Figure 8.3. The buffer measure then acts as a control chart, and the project manager can use similar action rules; that is, any penetration of the red zone requires action. Four points trending successively toward the red zone require action. Trending is especially important if your processes to produce project tasks are not in statistical control. Walter Shewhart  notes that the trend information is even more important in such cases.
Weekly Buffer History As Of 2/15/2002 9:41:07 AM Project: Puma_Ver_01 Milestone: Project End
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Longest Chain Complete
Figure 8.3 Measuring the trend of buffer penetration improves the early-warning aspect of buffer management.
Figure 8.4 illustrates the Concerto Software's project chain view. This view shows the tasks in order that are causing project buffer penetration, and the amount of buffer penetration. This tells the project manager where to focus buffer recovery.
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What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.