Below is a step by step example of how to determine gage bias. The example utilizes the
software package Measurement Assurance. Click here to download a free demo version of
Click here for the technical details of the determining gage bias in Adobe Acrobat format. For the same article in Microsoft Word for Windows 95 format click here.
To determine gage bias, a reference standard with a known value is necessary. Measure the part on the gage being tested a minimum of 10 times, and preferably more than 30 times. The greater the number of measurements, the greater the accuracy. In virtually every case, there will be bias, however, the bias may not be statistically significant. The significance is tested using the t-distribution, and increasing the number of measurements increases the discriminatory power of the t-test.
Input the measured values into the Gage Bias spreadsheet along with the reference value and the process variance and process tolerance if desired, click the Compute Bias button, and the bias study is complete. Click the print icon, and the results appear in the Report Writer. Right-click on the graph, and a tabbed dialog box appears that allows you to customize the graph.
Engineered Software, Inc.