Hi Tom,I am sure the Eldorado has the offset. Now, there is one easy way to tell and that is to test it. What you need is a piece of ferrite. A piece of magnetite rock will do, or even a small cheap ceramic magnet will work.
Just ground balance in the AM mode and don't add any offset so the detector appears to be ground balanced properly. Now, pass over the ferrite test target and you should get a strong negative response in the AM mode. By this I mean the detector will go quiet and follow with a "bang" once the object is passed.
If that occurs, then switch to the disc mode and pass over the object again. If there is no offset, the object will cause a strange sqauall type sound. If there is an offset, the detector will appear to ignore the ferrite. It really doesn't ignore it, but you can't hear the effects.
If there is no sound in the disc mode, then adjust the GB while passing over the ferrite while remaining in the disc mode. Turn the GB in the direction that would normally cause the audio to go silent as the coil is lowered, if testing in the AM mode. Continue to adjust the GB control until the detector begins to generate an audio response from the ferrite. Once the noise starts, you are very close to being ground balanced in the disc mode.
If you were to switch back to the AM mode with this new GB setting, you would notice that the detector will now generate a strong negative response as the coil is lowered. This will give you and indication of how much of an offset there really is.
Optimum depth capabilities will occur when the detector is ground balanced for minimal ground signal. So, when in the AM mode, the optimum is when the detector is properly ground balanced. However, in the disc mode, the detector will not be at optimum if there is no adjustment made.
Now, the down side of an optimum ground balance setting in the disc mode, where the ground signal will be minimal (if you could hear it), is a hotrock will now generate a false signal. Once again, this hotrock problem signal is why there is an offset to begin with.
Reg