Force control limits and center line to be constantmain topics how to
Force control limits and center line to be constant... > control chart Options > Limits
Charts X and R, X and S, X, R, S, P, Laney P', NP, U, Laney U', Moving Average, EWMA, CUSUM
When subgroup sizes are not equal, each control limit will not be a single straight line, but will vary with the subgroup size. The center line of charts for ranges and standard deviations also varies with the subgroup size. If the sizes do not vary much, you may want to force these lines to be constant. For instance, you could enter the average sample size as the subgroup size. When you use this option, the plot points themselves are not changed; only the control limits and center line.
For the CUSUM chart, you can force the control limits to be constant using CUSUM Options > Plan/Type.