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Can anybody kindly clarify the following content from MSA Fourth edition. Also, we have a molded plastic part with only 1 cavity. The dimesion between the parts are very close, so the process variation is also close to 0, which makes it impossible for GRR to be less than 10%, how to deal with this kind of situation? Many thanks in advance.

For Product Control situations where the measurement result and

decision criteria determine, “conformance or nonconformance to

the feature specification” (i.e., 100% inspection or sampling),

samples (or standards) must be selected, but need not cover the

entire process range. The assessment of the measurement system

is based on the feature tolerance (i.e., %GRR to TOLERANCE).

For Process Control situations where the measurement result and

decision criteria determine, “process stability, direction and

compliance with the natural process variation” (i.e., SPC, process

monitoring, capability, and process improvement), the availability of

samples over the entire operating range becomes very important.

An independent estimate of process variation (process capability

study) is recommended when assessing the adequacy of the

measurement system for process control (i.e., %GRR to process

variation).