TABLE OF CONTENTS The inevitable variations in process measurements comes from two sources: the manufacturing process and the gauge. Gauge capability reflects the gauge's precision, or lack of variation, but is not the same as calibration, which assures the gauge's accuracy. As it was emphasized on the numerous occasions, process capability measures the ability of a manufacturing process to meet preassigned specifications. Nowadays, many customers use process capability to judge supplier's ability to deliver quality products. Suppliers ought to be aware of how gauges affect various process capability estimates.
The gauge capability includes two parts: repeatability and reproducibility. Repeatability, (actually the lack of it), is the gauge's experimental or random error. This means that, when measuring the same specimen several times, the gauge will never return exactly the same measurement. Reproducibility (actually the lack of it) is the (often annoying) inability of several inspectors or gauges to arrive at the same measurement from a given specimen, i.e. the variability due to different operators using the gauge (or different time periods, or different environments, or in general, different conditions). To summarize we have:
Estimates for ? 2 repeatability and ? 2 reproducibility come from a gauge study, or an GR&R (gauge repeatability and reproducibility) study. Hradesky (1988), Barrentine (1991), Levinson (1995) and Montgomery (1997, 2001), among others, provide procedures for gauge studies.
Gauge capability is a gauge's ability to repeat and reproduce measurements. Its measurement is the % of tolerance consumed by (gauge) capability (PTCC). Montgomery (1991) refers to it...
