Theoretically there is no upper limit. But 1.33 to 1.67 is better. If it is greater than 1.67, it means that the process capability is too good or the upper and lower limits of the specifications are set unreasonably. If the CPK is 100 and the specification is appropriate, this indicator should not be examined as it is of little significance. Instead, indicators that may exceed the standard or be close to the specification limit should be examined.