A pie gauge is a device used to measure magnetic field direction. It is an octagonal flat plate composed of eight low- carbon steel sheets, similar to pieces of pie. The octagonal flat plate is copper coated from the back side to hide the joint lines. The device has to be placed on the tested piece during the magnetic powder application and magnetizing. With an adequate magnetic field, the indications perpendicular to the magnetic flux lines on the various sectors of the octagonal plate will appear.

In compliance with: ASME Sec. V − Art. 25-SA 275 − ASTM E1444