Theory of Constraints Handbook - James Cox Iii [61]
Review of Resource Buffers
A resource buffer adds no time to the project plan, but it is a vital part of the CC internal communications plan. It is a calendar event set prior to a Critical Chain task or path initiation so that the PM can inform resources when they should prepare to perform the task. To maintain a tightly planned project schedule, a Critical Chain task must be started as soon as its predecessor is completed. The duration of each resource buffer should be set based on the PM’s knowledge of the project resources and their requirements. Some project members will have comparatively inflexible line duties and will require more set-down and set-up time. All resource buffers, therefore, will not necessarily have the same alert time. Resource buffers are established and placed in the project schedule after the Critical Chain is determined and project and feeding buffers are in place.
Review of Scheduling Buffers
Like project and feeding buffers, a scheduling buffer has no task time, but logically is placed between projects to regulate the initiation of projects in a regulated manner. The buffer is used as an internal communications tool to prevent project overload and to limit ineffective multitasking. A SR is designated and scheduling buffers are placed between the SR tasks which staggers the different projects. The buffer size is determined by the PMO (or equivalent) and based on knowledge of the entire project portfolio schedule. If the SR does not have a task in a particular project, the other resources on the project should be examined for potential multitasking and a scheduling buffer inserted before the project is initiated.
Changing Priorities
Periodically, organization priorities will change to admit new projects and to de-emphasize, delay, or cancel projects. Resource managers and PMs need this information so they can establish work schedules.
Since resource managers and PMs typically have access to detailed project information, they may be assigned the task of preparing reports describing the consequences (both expected additional costs and opportunity costs) of changing priorities. Thus, the advantages and disadvantages of a change in priorities can be analyzed prior to a final decision.
External Reporting
External entities in the context of this section will include those that have no immediate and direct oversight of projects and include:
1. The board of directors, the executive committee, or equivalent governing body
2. Other organizations for whom project work has been contracted
3. Regulatory bodies
There are three general requirements for project status reports to external entities:
1. Contractual requirements such as the Earned Value Management System (EVS)
2. Non-contractual performance reports to project owners
3. Internal control schedule and scope reports to a project office or similar oversight entity
Project Planning, Deliverables, and Periodic Reporting
In general, the best information to provide in status reports is the buffer burn rate: the percentage of CC tasks that have been completed and the related percentage of consumption of the project buffer. If 25 percent of the Critical Chain has been completed but 40 percent of the buffer consumed, the PM most likely will be required to explain how this trend can be reversed and the project brought back under control.
The Earned Value System
The Earned Value System (EVS) is a set of 32 criteria established for control and reporting in project management. The criteria are organized into five sections with five in Organization, ten in Planning and Budgeting, six in Accounting Considerations, six in Analysis and Management Reports, and five in Revisions and Data Maintenance. Most branches of the U.S. Government (and other governments) require adherence to the criteria for major project contracts.32 The requiring entities have also published volumes on interpretation of the criteria and “guides” for their implementation. If PMs