Chart Preparation Exercise (2)

We will also make use of simplified calculation sheets which allow us to take a step-by-step approach to the calculation of control limits and Cp/Cpk. The first sheet covers all the calculations required for the control limits on the chart. You will need to print out a copy of this calculation sheet as well.

During the exercise, you will be asked to calculate each of the values on the sheet. Some of the results may need to be rounded to a particular number of decimal places. If this is the case, then you will explicity be told how many places to round the answer to. The general principles covering when to round are basically as follows:

• The value of the mean and the control limits are conventionally rounded to one more decimal place than the individual values. In this case, the values are whole numbers, so the mean and control limits should be rounded to 1 decimal place.
• Intermediate results, which are for use in later calculations should not be rounded (or not as much as the final values). In this exercise, intermediate results will only be rounded if they have more than 3 decimal places.
• The capability indices Cp and Cpk are conventionally calculated to 2 decimal places.