Hoffmann geodyna 44m error

Hello together, I recently got a Hoffmann geodyna 44m from an acquaintance, but it doesn’t work properly! As soon as I turn on the device, the gram display shows some wild values and fluctuates back and forth, although I don’t do anything. Furthermore, I don’t understand how this red display should work, since it doesn’t show anything! Does anyone have any idea about it or could they provide me with an instruction manual? ic