Dustin Harbin delves into the strange world of the Ames Lettering Guide, whose mysterious wheel and holes have long mystified non-acolytes:
Oh, bedeviling Ames Guide! How curious your strange shape, your myriad holes filled with murk and mystery. What–what??–are you for?? This is the oft-heard complaint of people trying to figure out the wild wooly trapezoid that is the Ames Lettering Guide. Myself included! But over the years I’ve gleaned some info from here and there as to its use; plus of course a fair amount of experimentation on my own to boot. Like most people, most likely.
An illustrated “how to” is in the link for those who wish to join the order.