To meet different requirements for indication acceptance, a schedule of indication ratings is provided in which the materials are classified into 6 quality grades, based on severity of indications (length and quantity). It is very important to grade the quality of materials. Too tough grading would waste material for those material which would otherwise be used are rejected, while too slack grading would lead to reject of finished products due to substandard material.

The principle for material selection are established: grade 1&2 material is used for critical components, grade 3&4 for important components and grade 5&6 for average components in order to use material efficiently. This reduces products cost and increase acceptance rate in magnetic powder tests.