The magnetic field indicator (also known as the octagonal test block) is made by welding eight low-carbon steels with copper sheets by electric furnace brazing. It has a non-magnetic handle, which is basically the same as the standard test piece, but longer than the test piece. Durable and easy to operate. For workpieces where the radius of curvature is small and the type A test piece cannot be pasted, the use of the magnetic field indicator is still valid. It is manufactured according to China's JB4730-94 standard and American ASTM E709 and ASTM A275 standards. It can check the comprehensive performance of the flaw detection equipment, magnetic powder magnetic suspension and the proper operation method, which can fully reflect the magnetic field strength and direction of the magnetized area. It has the advantages of intuitive magnetic display, convenient use, good contact, durable and good repeatability.