I'm about to try hardening some small parts with cherry red and a torch, since I don't think I can do the furnace thing. So after I'm done, I would like to check the hardness. I certainly am not going to go for a Rockwell tester. I saw these on the Bay: http://www.ebay.com/itm/TSUBOSAN-Ha...986884?hash=item3600c29804:g:w78AAOSwo3pWgobw Has anyone used them? On the other hand, do I need them at all? Will a simple file tell me (more or less) all I have to know? Happy new year, y'all!