Well, that pretty much shoots this discussion of VDI numbering down in flames, eh?
And there you have it, both extremes. VDI numbering and other forms of TID (Target IDentification) are not perfect - that is a fact. I beg to differ a bit, however, with the impression that they are of little use.
Air tests ARE of limited value in that they are contrived practice. The real world is indeed a different place than a laboratory. Lab practice is not utterly useless, though, as the pundits would have you believe. It helps one to establish some sort of a baseline, a practical neccesity when attempting to assign repeatability to real world occurence.
In other words, it IS a place from which to start.
Much of the time, under much of our detecting circumstances, the TID features of modern, up to date detectors are pretty darn good - down to about 6". There can be circumstances where this is compromised, sometimes even severely, depending on local condition. So it is the wise man who knows
both his location and his equipments limits.
Yet, when used within their limits, modern TID circuits are more accurate than you may be led to believe by their outspoken opponents. I recall when TID features first hit the scene. By those standards, today's equipment is light years ahead and is the fulfillment of a dream for most of us long-time detectorists.
So, don't be misled into believing that VDI and TID features are useless. Just know their limits and don't bet on them to be faultless.
PS - Here's a Detecting Rule Of Thumb for you:
When searching for gold, learn to love the midrange: nickle coins and all the useless trash we denounce.
Pulltabs, foil, canslaw, screwcaps, eraser ends, bottle seals... these are all the low-brow kin of gold and gold jewelry. It behooves you to go where gold jewelry is most commonly found, and then plan to dig everything at foil and above.
