Over the years, I've tried numerous ways through a combination of VDI and tones to better identify targets that were under my coil. It didn't take long for me to discover that trying to cut the tone and VDI distinction too fine in an attempt to accurately identify targets was unproductive. Through some trial and error, the obvious finally became clear.
VDI is not an exact science by any stretch. Target ID can be affected by numerous variables such as depth, soil composition, the metallurgical make up and orientation of the targets in the soil. Expecting a consistently exact value for each possible target was unrealistic. I finally concluded that what I wanted was only an indication of what might be under my coil rather than expecting or trying for a precise ID. Can VDI and Tones do that for me? Yes
After realizing what I wanted or needed from of a tone/VDI combination, I settled on a 3 tone option. Below are a few bullet points that summarize my case or reasoning for adopting that 3 tone solution.
~ My attempt at using 50 tones proved impossible for me...information overload! I then tried 5 tones and although much more understandable than 50, I felt that 5 tones was really unnecessary and might even be overkill. Why?
~ ALL targets fall within 3 categories/zones of conductivity of Low, Medium or High so it made more sense for me to focus on those 3 zones and then align the tones accordingly. The tones provided information on what zone I was dealing with while the VDI gave me some rough indication as to where that target fell within the range of that zone.
~ I also wanted a system that wasn't apt to cause me to ignore good targets because they were similar in make up to worthless targets. Example; gold and aluminum are both mid level conductors and generate similar VDI within that range, I therefore didn't want to exclude anything within the Mid or High level conductivity scale. Yes, I'll dig aluminum so as not to pass up potential gold and dig other high conductive targets so as not to pass up silver.
~ I tested quite a number common targets of varying size and metallurgical composition and came up with some common VDI ranges that I see on our beaches for each of the conductivity zones. I then modified the 5 tone option to 3 tones which suited me just fine for the beach hunting I do.
My results:
Low conductive targets ranged from -9 to 0 and I assigned it Tone level 1 (the old iron grunt)
Medium targets ranged from 1 to 18 so I chose Tone 12...a nice mid level tone
High conductors were 19+ so I gave them the highest Tone level of 25
To reduce five tones to three simply involves assigning the same tone for three zones of the five possible zones:
i.e.
Zone 1 = Tone 1;
Zone 2 = Tone 12;
Zones 3, 4 and 5 = Tone 25
~ In my work with a local museum however, the 2 tone option could also be used. When digging museum quality artifacts, iron is a valued metal so I dig everything. I also dig it all when I detect along Florida's Treasure Coast as remnants of the ships fall within the iron or low conductive range and are often times found along our beaches.
Just the view from my foxhole...your view may vary.