The electronics on a metal detector are programmed to ID a target which is coin sized. A large target or tiny one may not read accurately. All detectors have to deal with this issue. It's not that the detector read the target wrong, it's a case of the nail has the same conductivity as silver and that's what the detector read it as. This is normal and is common with all of us. As you get more proficient using your detector, you will learn the little tricks (not in the detector manual) which help identify junk.