All detectors are easily confused with iron when it's at depth. The discrimination works but only to a certain degree and only on targets closer to the surface. The best results for iron discrimination also require a Double-D coil to maximize on this feature. One half of the coil transmits to the target and the other half receives the information to process. The area where the coil loops overlap is where the emission field is deepest. I spent yesterday digging iron with a Double-D and was a little annoyed but that's the limitation we all have to endure. All of my targets were at depth so this added to the confusion. The soil had so much iron in it that it was the color of freshly dried blood. All are factors which hamper the detectorist.
Something else you mentioned is "depth accuracy". The results are the same regardless of detector brand and the reason they place this feature on the detectors is for the North American customers who (apparently) are "prone not to dig a target without a depth estimation". Whilst I'm amused to hear that my North American cousins need to be told how deep their target is before they will bother digging, I find the Garretts to be far less accurate than the estimation on the X-Terras. But each can be fooled. I can only give you the same advice as I give to others here: Just use it as an estimate. This is because there are so many factors in the soil and in the nature of the target that make it somewhat impossible to get a perfect reading on all targets... especially if the target is at depth. Sometimes we get very accurate readings for depth and the iron discrimination works perfectly (you can hear the threshold blanking out to inform you of an iron target) but there's also a lot of interference in the ground and around the target. All of which will confuse the sensors. In perfectly neutral soil without iron or salts, the results tend to be more accurate.
There's a few tricks you can pick up on this forum.... one of which I use regularly to determine if a target is iron before I dig it. Since I use my X-Terra for Prospecting for gold nuggets, I was initially surprised when "positive" Target ID's were turning out to be Iron. The technique I use is to scrape away the first layer of soil - about an inch - and then rescan the target. Often, the signal improves and the target is positively ID'd. But if the number's on the TID "jump around" in a randon way for each scan, then the target is almost always iron. If the numbers are in a consecutive order, or if they repeat (and are not in the negative range), the target is worth digging.
Usually, if you dig off the topsoil, the target clarity is much clearer and the ID is more accurate. You can then decide whether or not to dig.
* Just a related observation: In areas of high trash that I explored yesterday, I found a lot of unfilled holes. Some were very deep (GPX/SD detectors being used there). I don't know if this is because the detectorists were frustrated by lack of positive targets but it was very sad to see such large, deep holes hacked out of the ground and left that way. To everyone: Always fill in your holes.
