On my last detector if discrimination was set to a certain value, then any target with an id of less than that value was blanked out.
So on the Deus in Basic 1 for example, the discrimination is set at 10, so I was expecting any iron etc with an id of 10 or less, would get blanked out (ie. you would not hear it).
But with the Deus, discrimination works in conjunction with Iron Vol, some people still like to hear the response from iron, but possibly at reduced volume. This is where the Iron Volume control comes in.
If you don't want to hear a response from targets between 1 and 10, set Iron Vol = 0.
If you want to hear a faint response from targets between 1 and 10, set Iron Vol = 1.
If you want to hear a louder response from targets between 1 and 10, set Iron Vol = 2.
And so on until with Iron Vol = 5, you get a the same volume response as targets with an id of over 10.
See page 12 of the manual.
