My question was inspired by acquisition of grinding accessories pictured, from a retiring toolmaker. He said he’d made them all with the aid of a magnetic square. I should have asked him at the time if a magnetic square is considered necessary to produce the most accurate tools possible on manual surface grinders. But I didn’t. Anyway, that’s my question. We have a few surface grinders in the shop but haven’t used them much, but expect more grinding work this year. We don’t have an experienced grinder operator now. Also, if I buy a used mag square, is it likely to lose its magnetism, and if so, can that be restored?