Saw Set Tool (4-11 TPI) - Made in Japan

According to a piece of paper included, the numbers are for "anvil graduations" and do not correspond to tpi (ppi). What good are the numbers then?

Does the "4 - 12" refer to the angle that the tooth will be bent over to? Or are "4 - 12" number graduations based on pure whim?

What is the metal it is made out of?