I just acquired a lightmeter Gossen Lunasix F.

After learning how to use it, I realized there might be a calibrating problem. As a matter of fact, it looks like the measuring is one stop away (even 2) from the reading of another lightmeter camera (Nikon F80). Even the f16 rule doesn't seem to give equivalent results with the Lunasix.

I don't have shoot accordingly to the Lunasix F yet, so I unfortunately could not give shot samples.

Someone knows whether I could calibrate the Lunasix with the screw on the back. If so, how do I do it?