Hi Ken, I don't know think I can explain this fully, but let me give you an example of what I've discovered. Maybe someone can make better sense of it too.
When I was detecting for the Chinese coins, in the ground at any depth, some of them were giving me readings of -1 and -5. But when I dug them up, and swiped them under the coil, I got readings of +29. It dumbfounded me! The only thing that I can see why this would happen, is the composition of the metal varied. The coins that gave the negative readings were blackish in colour, for some reason they were affected by the wet or damp ground conditions, and had a lot more wear. The coins that gave a positive reading while underground, were green in colour, and didn't seem to have as much wear as the darker coins, happened to come from drier soil, and were in better nick. The same with English coins. I've found that those that were more worn and where the ground conditions affected them to the point that the metal was fairly corroded, they tended to give a negative number reading, whereas those that faired better, gave a positive reading. But this isn't true in every case, just seemed to do this quite frequently. With English coins, the pitch of the signal varied too, from deeper ones, where it left you wondering whether to dig or leave it be, much, to higher pitched, where you thought they were something worth digging. This is where I've learned to dig everything. I found that, somehow, ground conditions, mineralization due to rust from other objects "staining" the soil around the detected target, and a change in soil type, all seem to have a bearing on how the detector reads the information. I definitely believe that wet or damp conditions can have an adverse effect on targets, but can also bring "up" targets that would otherwise not be read by the detector, hence, after a rain, I often have better success. I've proved this to myself time and again. The flag badge in my prior post,came out of wet ground after a good rain. As for lifting the coil, it seems the detector readjusts itself, as if correcting itself from it's first initial reading. Generally where I detect, the signals I get are fairly true, so I don't find the need to lift the coin, but sometimes I do to verify what the detector first read, or because this very same thing you've mentioned, has happened. But I would study the ground your coins come out of, and look for differences in the soil type, or if there is a "stain", or other object that might what to "cloud" over the target you're pinpointing. Check your coin, the condition it's in, and maybe make a mental note for the next time. You can almost usually get an idea of what to expect. I hope somehow I've helped. It's just what I've gleaned from what I've experienced, and I'm just trying to find an answer too. Have to say, I love using all metal mode!
Cheers Angela

