I recently bought a broken Prema 6047 on ebay, fixed it and got in contact with the manufacturer to ask a few questions. (Which were answered competent and quick, even got a replacement part for free!)
But in the process of asking i got the information that the service technician responsible for fixing/calibrating these meters leaves the company mid november, and it is unknown if they continue to support these devices. (They stopped selling meters in 2002).
So just a heads-up for every Prema voltnut here, if you want your device calibrated by Prema(inhouse) you should arrange an appointment ASAP!
Let's hope they hire another service technician which will service these wonderful meters...