The inner limits set on a control chart in a production process. If the observed value falls between the warning and action limits, then it is taken as a signal that the process may be off target, and another sample is taken immediately. If it is also outside the warning limits, action will be taken, but if the second observation is within limits, the production is assumed to be on target. For the means of samples of size n in a process with standard deviation σ with target mean μ, the warning limits will be set at