Book Excerpt: " Checkable Iron Signal Differences "

[cjc]

A machine with the sophistication of the Equinox is much more readily able to identify iron by how it responds on the cross-sweep. This is because iron is more like the ground than a non-ferrous target. You could say that it is fully “grounded.” Many larger iron objects will sound off well from the standpoint of the first target sweep but when you check them on the cross sweep they lack consistency. In effect the detector is reading an interaction between ground and metal--rather than just metal. This interaction is not stable or “complete” in the same way as a solid, consistent target like a coin or ring. You could say that the detector is reading a changing “process.” With a high gain detector like the Equinox, understanding this one simple bit of theory will save a lot of digging. 
Another basic method to get a better idea if a signal is iron is to simply compare how loud it is with the depth meter reading. A blaring response that reads full depth is probably something larger than a coin or ring. 
As well, where you see a response that seems to change location or needs to be “coaxed” to give a response--suspect iron. In that some of the Equinox’s more complex iron muting features (Iron bias) can reduce depth, having a good command of these inherent, checkable differences between an iron signal and a non-ferrous one can help your accuracy a lot. 
Picture Caption:
Basic signal quality differences: ferrous (L) versus non-ferrous (R). This is how the well-known bottle cap ”tell” method of removing the coil to produce a low tone works. Whereas a good target is either heard or not, a cap has a surrounding field that produces a low tone.
From: “The Minelab Equinox: From Beginner to Advanced”
By Clive James Clynick

[Mark Gillespie]

40 minutes ago, cjc said:

A machine with the sophistication of the Equinox is much more readily able to identify iron by how it responds on the cross-sweep

This is a good point, the Equinox is very good at discerning multi sweep target identification.