Today I air tested the SUM tones on coins and on pieces of trash and found there is more than 9 tones in SUM. For example, a pulltab with beaver tail gives a certain tone. Break off the tail and the two pieces give different tones but they still fall into the Pulltab catagory. I counted 14 tones in SUM from the coins and trash that I had, but all those tones are squeezed into the 9 target catagories that is on the meter, so each catagory can have more than one tone. Now, no way could I remember all those tones and targets but what I learned is when the target conductivity changes even a little then the tone pitch changes with it, and that the SUM mode might even be capable of more than the 14 tones I got. Then I did a masking test (in Disc mode with knob set at Iron) with a large piece of iron close to a silver dime. When going directly above the iron and then over the dime in the same sweep, I could hear the dime signal break through. But when sweeping above the dime only, without going directly above the iron, then I heard no dime signal. So, as they say, it's best to sweep over the iron from different directions to be able hit the coin just right. Right or wrong, this is what I gathered from these tests.