Attribute Control Charts
Attributes control charts plot count data, such as the number of defects or defective units against the sample number.
NP and P Chart
The NP and P Charts are control charts for defectives. NP chart tracks the number of defectives and P charts tracks the proportion of defectives (number of defectives divided by the subgroup size). They are used when you can compare a product to a standard and classify it as being defective or not.
C and U Chart
The C and U Charts are control charts for defects. C Chart tracks the number of defects and U Chart tracks the number of defects per unit sampled. They are used when a product is complex and a product can have many defects. For example, C Chart can be used to chart the number of defects on a carpet and U Chart can be used to chart the number of defects per square metre sampled.