Critical Chain

A buffer is anything that puts distance or protection between two potentially conflicting elements, such as a jacket providing a buffer against cold weather. In Critical Chain, buffers are used in production to protect a system from breakdowns, bottlenecks, and inventory issues, such as allowing a buffer of resources to build in front of a bottleneck process to ensure continuous operation of the bottleneck. Richard’s class discovers that buffers can be used in project management to protect specific steps and tasks, as well as the critical path, itself, by using buffers of time to protect against delays.

Broadly, Critical Chain Project Management, or CCPM, is a method of project management that seeks to efficiently manage resources and scheduling to shorten lead times and maintain quality without exceeding budget. The critical chain is the longest chain of dependent steps in a project, considering various constraints and resource contentions that might otherwise negatively impact the critical path of the project. By managing with such constraints in mind, the critical path can be protected from constraints, allowing the project to progress unhindered.

The critical path of a project is the longest chain of steps in terms of time, while noncritical paths are shorter chains of steps, or they are steps that feed into the critical path. Critical paths are often shown using PERT or Gantt charts, which are like flowcharts that measure the time and order of tasks in a project. As such, the longest path of tasks in a PERT or Gantt chart is easily identifiable as the critical path. Any delays to the critical path are delays to the overall project, and much of Critical Chain focuses on how to protect the critical path from delays.

A constraint is a limitation on a process or situation, such as how budget limits the amount of money that can be spent. Constraints are conditions that must be accounted for in project management because they present hurdles to efficient progress, but not all constraints have an equal impact on the overall project. In Critical Chain, TOC is used to identify the biggest constraint, which is then used, ideally, to encompass multiple issues in a system, and the alleviation of the biggest constraint is assumed to have the greatest benefit for the system.

The evaporating cloud technique involves the comparison of two seemingly contradictory elements in a process. This process is shown as a diagram showing how the two elements contribute to a common goal, and it is used to evaluate the assumptions that underpin each element to see where a flaw in reasoning may be influencing the system. The evaporating cloud between the “cost world” and the “throughput world” is how Johnny uncovers flaws in cost evaluation that allow for TOC to produce results in production.

Lead time is the total time a task or project takes to complete, defined as the time from the start of a task or project to the completion of that task or project. In Critical Chain, lead time is the focal point of most of the thought and effort of the novel, with characters consistently trying to shorten lead times for individual steps and for projects overall. Shortening the lead time on a project means an earlier completion, which in turn allows for earlier operation and greater profit and output.

A project is any effort that can be broken into individual steps contributing to a singular goal. Richard struggles to define project in accessible terms for his class, noting that academics tend to provide lengthy definitions. Project management, then, is the process of determining how to arrange resources, time, and tasks over the course of a project to increase efficiency, decrease cost, and shorten lead times. Critical Chain is an extended discussion on how projects function and how best to manage projects to achieve these goals.

Subordination is the process of ranking tasks by importance and making less important tasks dependent on the conditions of a more important task. In TOC, subordination is the prioritization of a constraint, followed by the arrangement of other tasks and resources based on that priority. If a bottleneck is identified as the biggest constraint, for example, then all the tasks feeding into that bottleneck must be arranged to maximize the bottleneck’s efficiency, therein subordinating the feeding tasks to the bottleneck.