H Desert Digger: said:
Does anyone know why Minelab has the -9 thru 40 target ID system when a lot of the other companies seem to use the somewhat "standard" 0-99 target ID?
After a few yeas on the AT Pro, I find myself getting lost with the Nox's Target ID numbers.
HDD
Knowing 'WHY' a lot of manufacturers do some of the things they do has always been a bit puzzling. Matter-of-fact, it's also a mystery why some engineered designs
don't do some things, or why they omit some features, modes or functions on a detector.
Your question points to one of the more uncommon things we all learn to figure out along the way. Minelab hasn't always used a -9 to +40 VDI reference, and not all manufacturers use a 0-99, either. There is no 'standard' as such but it would be nice. Take my White's XLT , for example, that uses a VDI range from -95 to +95 which makes 191 VDI numbers, when you include the '0' at mid-point. My 'Bushwhack' program accepts all Disc. 'segments' or 'notches' or 'VDI Numbers' from -40 up to +95.
The MX Sport and MX-7 also use the -95 to +95 scale, but the '0' is off to the left because the -95 to '0' has a more compressed scale and the '0' to +95 is a more open or broader scale.
Then you have others that rely on that '0' to '99' scale you mentioned, but they have different numeric VDI readouts or assignments. My Fisher F5 has the Ferrous / Non-Ferrous break at '15' as does my Nokta / Makro Simplex +. But my Nokta FORS CoRe has that break-point at '40', the Nokta FORS Relic at '20' and the 'Makro Racer 2 at '10.'
The Teknetics T2's have a Ferrous break-point at '40' as do their Omega 6000 and Omega 8500, but all three of then have a different Iron Nail rejection point. Using the same three iron nails for comparison, the Omega 8000 rejected them with a VDI of about '16'-'17' and the T2's at about '21' while the Omega 8500 needed an increase to about '37' to '39' or almost the Ferrous break-point.
A US 5¢ coin makes a very good test target, too. I look to see where each detector model I use registers them on
THEIR VDI scale in an 'air test' or on the ground in a metal-free area. That gives me a rough or general idea how a particular desired target, of a uniform size, shape and alloy content,
might register in an ideal condition and within a reasonable coil-to-target distance .. better known as 'depth.'
The next step is so simulate in-the-field encounters you have made, or perhaps make up some tests of what you think you might come across, and always be inquisitive when out detecting of any suspicious signals caused by good targets and a masking target. For example, I have a US Nickel I can look at, but when I sweep the V-540 over it I get a rock-solid lock-on that is almost always '15'. In a series of perhaps 7 to 9 passes I might get a '14' but the rest of the time it registers '15', and that is not what you'd expect from a 5¢ piece.
Why? I duplicated an in-the-field encounter I made at a RR ghost town of an 186? Shield Nickel that I eyeballed on-the-ground but the response was good on my unit, but didn't respond to my friend's detector. The cause? A RR spike was directly below the coin an inch of so, and he used a different older model with more Discrimination that I did.
On that particular test I was doing yesterday, the V-540 did give a tighter and closer-to-correct VDI than some of my other models, but it was still an errant, higher read-out.
I DO like the EQ. and Vanquish VDI display, and I also know it can be closer in many cases than other brands and models, but it can also be wrong quite often, too. In the end, having an assortment off makes and models helps keep me on-my-toes to remember the differences in design and read-out of desirable targets from model-to-model because they can differ.
Monte