Critical Chain Monitoring

According to proponents, monitoring is, in some ways, the greatest advantage of the Critical Chain method. Because individual tasks vary in duration from the 50% estimate, there is no point in trying to force every task to complete "on time"; estimates can never be perfect.

Instead, the buffers created during the planning stage are monitored.

Managing buffers

Managing buffers is the key component of tracking a Critical Chain project. But because task estimates are uncertain, Project Managers should not apply exact measurement techniques such as variance analysis and earned value to tasks.

Instead, the Project and Feeding buffers should be monitored regularly, and the Project Manager should act according to how much of the buffer has been penetrated by task slippage.

Each buffer should be treated as if it were divided into three equally-sized regions:


Conceptually, the first third is the green zone, the middle third is the yellow zone, and the last third is the red zone.

  • If penetration is into the green zone, or if there is negative incursion (tasks finishing early), no action is required.

  • If penetration enters the yellow zone, the problem should be assessed and various courses of action considered.

  • If penetration reaches the red zone, corrective action should be taken. Corrective action could include finding ways to finish uncompleted tasks in the chain earlier or accelerating future work in the chain to bring buffer penetration back out of the red zone.

Reviewing the Fever Chart

A fever chart or similar graph can be created and posted to show the consumption of buffer as a function of project completion.


If the rate of buffer consumption is low, the project is on target. If the rate of consumption is such that there is likely to be little or no buffer at the end of the project, then corrective actions or recovery plans must be developed to recover the loss. When the buffer consumption rate exceeds some critical value (roughly: the rate where all of the buffer may be expected to be consumed before the end of the project, resulting in late completion), then those alternative plans need to be implemented.

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