If a GRR study meets the “correct” level of performance, does that mean the measurement system is totally acceptable?
Not necessarily. GRR only covers the amount of variation due to measurement error, and technically only covers the short-term results gained from one study. This study also may not include all the sources of variation that can affect the measurement system over time, such as environmental effects, lot to lot differences, etc. GRR also covers only one characteristic, one of perhaps several characteristics in a total measurement system. Similarly, the Ppk or Cpk index covers only one characteristic of a part or process – a “good” Ppk or Cpk index does not necessarily mean the entire part or process is acceptable. Also, GRR does not cover bias, linearity or stability issues since it does not generally study the measurement process over a long period of time.
