Gauge Stability

The BIS.Net Team BIS.Net Team

The objective of a Gauge Stability Study is to see how consistent repeatability and bias is over time.

Historically this has been done with Control Charts.

On a periodic basis, daily, weekly, or monthly take a convenient number of readings, such as 5 and plot the bias on a standard X-Bar and Range or Sd chart. If there are no out-of-control signals the process is deemed to be stable. Out-of-control points on the x-bar charts indicate instability with bias. Out-of-control points on the Range/Sd charts indicate instability with repeatability.

Used to study bias stability
Used to study repeatability stability

An alternative stability analysis can be performed with Dynamic Process Performance charts which show changes in bias, and repeatability on the same charts, such as shown below.