SKEDSOFT

Note that the shape of the operating characteristic is a reflection in a vertical line of the typical shape for an attributes scheme. This is because, in this case, the good batches have large mean values whereas for attributes good batches have small proportions of non- conforming items.

An operating characteristic for percentage impurity, where a good batch has a low mean, would have shape shown opposite.

In other cases, such as the diameter of screw caps for bottles of vinegar, the mean of a good batch must be neither too big nor too small and the shape of the operating characteristic would be as shown in the diagram on the right.