Discrimination Settings on Metal Detectors: A Complete UK Guide
One of the most underused and misunderstood features on a modern metal detector is the discrimination control. Whether you are swinging a budget machine across a ploughed field in Suffolk or running a high-end multi-frequency unit along a Permission in Yorkshire, understanding how to set your discrimination correctly can be the difference between a productive day and a bag full of ringpulls. This guide walks you through everything you need to know about discrimination settings, how they work, what to reject, and — crucially — what you should never reject when detecting in the United Kingdom.
What Is Discrimination on a Metal Detector?
Discrimination is a feature that allows your metal detector to filter out certain types of metal by their conductivity and ferrous properties. All metals conduct electricity to some degree, but they do so at different rates. Iron, for example, is highly ferrous and sits at the low end of the conductivity scale. Silver and copper sit near the top. Your detector assigns a numerical value — known as a VDI (Visual Display Indicator) or Target ID number — to each signal it receives, and the discrimination control allows you to choose which numbers trigger an audio tone and which are silenced.
In practical terms, this means you can tell your machine to ignore iron nails but alert you to a hammered coin. Or you can set it to ignore everything below a certain threshold while still responding to a Georgian silver shilling. The challenge — and this is where most newcomers go wrong — is that discrimination is not a perfect science. Targets overlap. A small gold ring can read similarly to a pull-tab. A large iron fragment can, under certain soil conditions, mimic a high-value target. Understanding these nuances is essential to detecting success in the UK.
How Discrimination Works in Practice
Ferrous and Non-Ferrous Targets
Most detectors divide targets into two broad categories: ferrous (iron-based) and non-ferrous (everything else). The basic discrimination control on entry-level machines like the Garrett Ace series or the Minelab X-Terra range simply allows you to set a cut-off point on a scale, typically 0 to 99, below which the machine will not respond. Set the discrimination at zero, and you hear everything. Raise it to 40, and most iron will be silenced. Raise it further and you start losing low-conductivity non-ferrous targets — including, critically, some gold.
Notch Discrimination
More advanced machines offer notch discrimination, which lets you select specific segments of the ID scale to accept or reject rather than simply setting a single threshold. This is standard on machines such as the Nokta Makro Legend, the Minelab Equinox series, and the XP Deus II. Notch discrimination allows you, for example, to reject the ringpull zone (typically around 12–15 on a 0–99 scale on many machines) while still accepting the segments above and below it.
This is particularly useful when working fields that have been used for recreation, as sites near old fairgrounds, picnic areas, or wartime camps in the UK tend to be littered with ringpulls and silver foil from decades past. Being able to surgically notch out that segment without losing neighbouring conductivity ranges is a significant advantage.
Multi-Tone Audio
Alongside visual discrimination, most mid-range and high-end detectors use multi-tone audio to help you assess targets before you dig. A low grunt typically indicates iron. A mid-tone might suggest a small non-ferrous target. A high clear tone is usually a high-conductivity target such as a silver coin or a copper item. Learning your machine’s audio language is just as important as understanding the numbers on the screen, and experienced UK detectorists often trust their ears over their eyes.
The Unique Challenges of UK Soil and Sites
The United Kingdom presents some specific conditions that affect how you should approach your discrimination settings. If you are detecting in Wales, Scotland, or parts of the north of England, you may encounter highly mineralised ground — particularly in moorland and upland areas. This ground mineralisation creates what is known as ground noise, and it can cause your detector to behave erratically, especially on lower discrimination settings.
Similarly, sites that have seen heavy agricultural use — which describes the majority of productive arable land in England — will contain enormous quantities of iron in the form of harrow tines, horseshoe fragments, cut nails, and general farm debris. Fields in East Anglia and the East Midlands, areas rich in Roman and medieval history, can have staggering amounts of iron trash that will overwhelm a detector set to full sensitivity and zero discrimination.
Coastal and Beach Detecting
For those working beaches along the British coastline — from the Northumberland coast to Chesil Beach in Dorset — saltwater adds another layer of complexity. Wet salt sand is highly conductive and can generate false signals on machines not designed for the environment. If you are detecting a wet sand beach, you will generally need a detector with a dedicated beach or salt mode, such as the Minelab Equinox 900 or the Fisher CZ-21. These modes adjust the ground balance and discrimination settings to compensate for the conductive properties of salt. Do not try to apply the same discrimination settings you use on a dry inland field to a saltwater beach — the results will be frustrating.
What to Reject and What to Keep: A Practical UK Guide
Iron: The Great Debate
The instinct of most newcomers is to reject all iron immediately. It is understandable — iron is common, heavy, and rarely valuable in isolation. However, many experienced UK detectorists — particularly those targeting medieval sites and Roman agricultural land — advocate for running low discrimination or even all-metal mode for specific reasons.
First, significant historical objects are sometimes made of iron. Medieval buckles, Roman military finds, Saxon artefacts, and early medieval trade weights can all be ferrous. The Portable Antiquities Scheme (PAS), which operates across England and Wales and encourages the voluntary recording of archaeological finds made by members of the public, has logged thousands of iron objects of historical and archaeological significance. If you discriminate out all iron, you may be walking past important finds without knowing it.
Second, a phenomenon known as iron masking occurs when a high-value non-ferrous target sits in close proximity to an iron object. The iron can cause the detector to interpret the combined signal incorrectly, either silencing the good target or causing a confusing mixed signal. Running lower discrimination and learning to interpret mixed signals is a skill that pays dividends on ancient sites.
A reasonable compromise for most UK arable detecting is to set discrimination just high enough to eliminate the most obvious large iron targets — large fragments that produce a solid, repeatable low grunt — while digging anything that sounds uncertain or mixed. This approach is time-consuming, but productive permissions in England rarely reward laziness.
Gold: The Problem Zone
Gold is the target most detectorists dream of finding, but it sits in one of the most problematic areas of the conductivity scale. Depending on the purity and size of the gold object, it may read anywhere from the upper iron range all the way up to mid-range non-ferrous. A small Tudor gold coin may read similarly to a gold ring, but a tiny gold fragment or a thin gold wire object may sit firmly in a zone that many detectorists have discriminated out.
The implication for UK detecting is clear: if you are working a site with any possibility of gold finds — and given the depth and breadth of British history from the Bronze Age through the Saxon period and beyond, many permissions have that potential — you should be running low discrimination and digging mixed signals. Many of the spectacular gold finds recorded through the PAS and reported under the Treasure Act 1996 were made by detectorists willing to investigate uncertain signals.
The Treasure Act 1996 is central to UK metal detecting practice. Under this legislation, finds of gold or silver that are over 300 years old (with some exceptions), along with associated objects and prehistoric metalwork, must be reported to the local coroner within 14 days. Failure to do so is a criminal offence. This is another reason why running low discrimination matters: you cannot identify something as Treasure if you never dig it up.
Ringpulls and Foil
These are the bane of detecting in the UK, particularly on sites that have seen recreational use in the 20th century. Ringpulls from aluminium cans typically read in the mid-range on most detectors, often overlapping with the gold ring zone. Silver foil sits lower on the scale.
On sites where you are confident the likelihood of gold is low — a productive medieval arable field, for example, where your primary targets are hammered silver coins and copper-alloy artefacts — notching out the ringpull zone is a reasonable approach. However, on any site where gold is a realistic possibility, most experienced UK detectorists accept that they will be digging ringpulls. Consider it the price of thoroughness.
Lead
Lead is extremely common on UK agricultural land. Medieval lead cloth seals, Roman lead weights, lead fishing weights, musket balls, and scrap lead are all regularly encountered. Lead reads low on the conductivity scale — often in the range that beginners discriminate out. This would be a mistake. Lead cloth seals recorded through the PAS number in the tens of thousands, and they are genuinely historically significant objects. Medieval lead objects, Roman lead ingots (known as pigs), and even Saxon lead spindle whorls are recorded regularly. Dig the lead signals. Learn to identify them by their characteristic soft, low-mid tone on most machines.
Recommended Starting Settings for UK Conditions
General Arable Fields (Ploughed Agricultural Land)
For a typical arable field permission in England — say, a wheat or barley field in Lincolnshire or Kent that has a history of Roman or medieval occupation — a good starting point is as follows:
Moving Forward
Once you have the fundamentals in place, the possibilities open up considerably. The UK offers fantastic opportunities for anyone interested in this hobby, and with the right foundation you will be well placed to make the most of them.
