The ferrous numbers will sometimes be different in the ground because of mineralization and other ground conditions. I've learned it's the conductivity number that is more consistent. If I get a high toned signal with conductivity over 40 I'm going to dig it no matter what the ferrous number is. Good targets seem to fall on the ferrous 12 line consistently when air tested. But, as I have learned, they can be different in the ground. Dig all the high tones and don't worry about digging some trash. You can't get around that no matter which detector you have. Focus more on the sounds and less on the numbers. Dig some of those iffy signals too. If I have iron discriminated out, I'm diggin' all those high tones! With this detector I have consistently dug more coins than trash every time I've hunted with it. It has performed much better than my other detectors in that regard. But, I did dig some screw-tops, can slaw and pull-tabs - not many, but a few. If I swung my coil over the ground and got a consistent 28-48, I'd dig it. That 48 conductivity number would get me excited. Most other detectors only measure conductivity. Look at the ferrous number as a little bonus that can help you decide whether to dig or not. Often it is more consistent...like with nickels. I don't know why, but f the ferrous numbers are 10, 11, 12 or 13 and the conductivity is 11, 12 or 13, I know it's going to be a nickel. Focus on the high tones and the conductivity number. Shoot, with iron discriminated out wouldn't you be interested to see what gave you a conductivity number of 48? In your case it would have been a quarter.