Chart Preparation Exercise (2)
We will also make use of a simplified calculation sheet which allows
us to take a step-by-step approach to the calculation of control limits
and Cp & Cpk. You should
print
out a copy of the 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.