It dosent look like the 'blade' is notched or engraved so the usuable part is the measurements on the pad. Is it cast or just black steel? Looks about the 1950's.. shouldnt be too hard to find out what it is. I should know what it is by the morning. :)
That sort of thing is really cool.. I inherited a box of things like that and I dont know what half of them are, although I did just unearth a magnificant solid carved brass chalk line dating back to the 30's. Im better with that stuff than I am with computers.
Which reminds me, I came in tonight with a Mac issue..better get it posted and see if the guys can help. :D