The Pie Gauge is a specialized tool used in Magnetic Particle Inspection (MPI) to quickly and easily verify the direction and presence of a sufficient magnetic field on the surface of a ferromagnetic test

The primary function of the Pie Gauge is to serve as an aid in determining the direction of the magnetic flux (field lines) on a surface. This is critical because MPI can only detect discontinuities (cracks, flaws) that lie roughly perpendicular (at 90 Deg.) to the magnetic field.