Help with Old Super 8 Camera

I recently recieved a Vivitar Tl 6 Super 8 Camera, and a fter some cleanup and a new pair of batteries I am ready to go. Except, for the Aperture. There is an auto setting that doesn't work, and the manual aperture control is a dial with no markings, so I can't tell what fstop is what. Does anyone have a suggestion on how I may figure out my cameras performance? I am thinking about buying some film, marking of every so mm, and then film short bursts depending on light, and then see how it comes out when developed. Seems kind of crude, but is there a better way :?: