Calculate mean and upper and lower control limits, using the links below for the appropriate Control Chart.
Calculation for Average and Range Control Charts
Calculation for Individuals and Moving Range Control Charts
Calculation for Standard Deviation Control Charts
Calculation for Proportion Defective (p) Control Charts
Calculation for Number Defective (np) Control Charts
Calculation for Number of Defects (c) Control Charts
Calculation for Defects per Unit (u) Control Charts
A Pareto Chart indicated that the development department made most mistakes, and a survey indicated that they did not understand the form. On the 15th of the month, a half-hour training class was held for the development people. The table and illustration below shows the calculation and Control Chart for the month. It can be seen that after the training, there were nine points in a row below the center line indicating a statistically significant improvement.
In the next month, the proportion defective was further reduced by extending the training to other departments. Before long, there were so few wrongly completed purchase forms that the subgroup period had to be extended to one week.