Hi, I just received my GMC-300 yesterday. Bought via ebay.
At first, it looks like working normally, reading 0.12uSV/hr or something like that. But, after a few hours, it reads like this... 14,615CPM and 4.872 mR/h right on my desk. It does get same huge reading after factory reset.
What's wrong with this unit? Should I send it back for repair? (I'm living in South Korea tho).