A manufacturer of high-performance automobiles produces disc brakes that must measure 322 millimeters in diameter. Quality control randomly draws 16 discs made by each of eight production machines and measures their diameters.

This example uses the file brakes.sav. Use One Sample T Test to determine whether or not the mean diameters of the brakes in each sample significantly differ from 322 millimeters.

A nominal variable, Machine Number, identifies the production machine used to make the disc brake. Because the data from each machine must be tested as a separate sample, the file must first be split into groups by Machine Number.