Brian, over in the UK, stated: "the more ferrous the soil, the less disc"."
He was referring to the "ferrous" or "iron mineral content" that is associated with a lot of their soils. In others words, it's non near neutral to mellow like a Florida coast beach, or easy-going mild ground such as a bulk of Texas dirt. Instead, a good deal of the plowed fields they hunt have a little more mineralization, iron mineralization or ferrous mineralization, whichever term you prefer.
If you are working a picnic area with an abundance of pulls tabs and screw caps, you would use a higher discriminate setting to reject (ignore) them.
If you were searching a ghost town that was littered with densely-strewn iron nails, then you would use just enough discrimination to reject or ignore the most common annoyance, the iron (ferrous) nails.
But when searching ANY site where you want to find-it-all, especially where there are known small and thin targets, you use NO discrimination to reject man-made objects, ferrous or non-ferrous.
Instead, you will want to use the least amount of discrimination possible ... preferable NONE (if your detector offers that option) so that all you are going to be doing is ignoring the very low-conductive ground signal. That way, ALL detectable target might be able be heard, then recovered.
With the Classic III SL or the Classic IDX/IDX Pro (same Classic III SL circuitry except with TID circuitry added), you have that capability. You simply want to make sure the Frequency Shift is set at the Factory Preset (ALWAYS unless you plan to adjust the GB as necessary), toggle to "Black Sand" and then set the Disc. Level at the minimum setting.
The Normal/Black Sand toggle simply adjusts the discriminate range by enhancing or expanding it lower when set at Black Sand. The upper rejection level is unaffected. Only the lower end is expanded.
If you have a properly set Ground Balance, then the Classic III SL or an IDX Pro can be one of the most efficient detectors you could own ...... for any application!
Enjoy England!
Monte
PS: If you have any particular questions about the Classic series, feel welcome to drop me an E-mail to: MonteVB@comcast.net
Monte