It's a rebadged Metrawatt:
Here's the complete manual:
http://www.rainers-elektronikpage.de/DIGITAVO.pdf
The cheesehead screws helped me close in on it. I have a Metrawatt Freq. Counter, Nixie type, all germanium inside, and good to a whopping 500Khz.
sprechen sie deutsch?? I might have a resource - a retired Navy Electronics Tech, born in Germany and fluent in electronics and German.
Cheers,