Most nulls will be iron, but not always. It will take you some time to get the feel/ear for it.
Les: I usually hunt in the discriminator mode, with a minimum discrimination setting of 1 (the lowest you can go on a stock Excalibur ll 1000).
, If I understand it correctly, the Excalibur Nulls (no threshold) under two conditions in the discriminator mode:
1: When it positively identifies iron
2 : It initially tones when it detects a non ferrous target or a false signal and nulls when it cannot confirm that target.
After it Nulls ( No threshold) the threshold tone will be that of the next item it detects:
If it is high pitched: it is a highly conductive target such as copper or hopefully silver.
If it is lower pitched: it could be aluminum or hopefully gold as they are less conductive
Usually it comes back with an annoying grating sound, which can be hunted with,
Most hunters reset the tone by moving the coil near the basket of their scope, It is better to reset it with a nickel as it is closer to the tone of gold.
A low threshold setting, barely audible - like the buzzing of a bee, is easiest on the ears.
Over several minutes, I have noticed that the threshold on my Excal, drops below audible, and has to be increased.
I have never been able to determine why - It could be a result of tired ears (you hear better when you first start out).
I usually have to continuously slightly adjust the threshold setting (about every 5 to 15 minutes - even if there are no targets).
As a result mounting the control pod on my back is impractical.