This pic has been floating around and I don't know who gets credit, but notice a couple things mechanical/machine doubling is flat and shelflike (pic could be better, but you get the idea). Another thing to notice is that the mechanical doubled letters are usually thinner or smaller than normal letters. If you haven't already done so, read the section on "worthless doubling on this site. http://doubleddie.com/58222.html (it's probably good to read the other tabs as well). The explanation along with the pics should start to clarify things a little
