Obtaining control limits

It is important to evaluate control limits from the mean and standard deviation of values from the process when it is in control. The process should be monitored carefully (to avoid special causes) for this training period.

Charge weight of insecticide dispensers

Consider an industrial process manufacturing insecticide dispensers. Among other measurements relating to the quality of the dispensers, it is important to keep the charge weight of the dispensers within fairly tight limits.

Drag the slider to the right to show the successive charge weights of dispensers that were sampled from the process output over a period of two days. We will treat these data as a training set and use the mean (463.66) and standard deviation (16.94) from these initial observations to obtain control limits for further data.

Drag the slider to observe the charge weights of the next 99 dispensers that were recorded in the following two days.

What are your conclusions about the process?

Is the process conforming to the distribution that was observed earlier? In what way has it changed?