If you’re new to metal detecting, one of the first things you’ll probably notice is the number that appears on your detector’s screen when you pass the coil over a target.
One moment you might get a low number, the next a much higher one, while another target may seem to jump between several different readings.
But what do those numbers actually mean – and can they really tell you what’s beneath the ground?
These numbers are commonly known as Target IDs, sometimes referred to as VDI (Visual Discrimination Indicator) numbers.
They can be extremely useful, but they are also one of the easiest detector features to misunderstand.
The important thing to remember is:
A Target ID is an indication of how your detector is interpreting a target. It is not a guaranteed identification of the object.
Understanding that distinction can make a big difference to the way you detect.
What Is a Target ID?
A metal detector transmits an electromagnetic field into the ground through its search coil.
When that field encounters a conductive object, currents are induced within the target. The target then produces its own electromagnetic response, which is detected by the search coil.
The detector analyses characteristics of that response and uses them to assign a numerical Target ID.
The result gives the detectorist additional information that may help distinguish between different types of targets.
Conductivity plays an important part, but a target’s response is also influenced by factors such as its size, shape and orientation.
That means Target ID should never be viewed as a simple measurement of the type of metal beneath the coil.
What Do the Numbers Mean?
Broadly speaking, detectors organise target responses across a numerical scale.
Depending on the machine, ferrous targets may occupy a particular part of the scale while non-ferrous targets are further separated according to their detected response.
The exact arrangement varies considerably between detectors.
This is important because there is no universal Target ID scale.
A number on one machine does not necessarily mean the same thing on another.
Even detectors made by the same manufacturer can use different Target ID ranges.
For example, Nokta’s original LEGEND uses a 60-point Target ID system, while the newer LEGEND 2 uses a 99-point scale.
The principle is similar, but the numbers themselves are not interchangeable.
Can a Target ID Tell You Exactly What You’ve Found?
No.
It can give you useful information, but it cannot reliably tell you exactly what an object is before you dig it.
Two completely different targets can produce similar responses.
For example, certain pieces of aluminium can fall into similar Target ID areas to desirable non-ferrous targets.
Gold is a classic example.
Small gold items can produce relatively low or mid-conductive responses and may overlap with foil, pull tabs and other everyday rubbish.
This is why simply memorising a list of “good numbers” and “bad numbers” can lead to desirable targets being ignored.
Why Different Metal Detectors Give Different Target IDs
Manufacturers use different Target ID scales, processing systems and display methods.
Some machines use relatively compact numerical ranges, while others divide target responses across much larger scales.
Certain detectors also provide additional information beyond a single number.
For example, Minelab’s MANTICORE uses a two-dimensional identification map that plots target responses using conductive and ferrous information rather than relying solely on a single Target ID.
XP, Nokta, Garrett and Minelab also each have their own approaches to target identification and audio.
This means an online Target ID chart should only ever be treated as a rough guide – and ideally it should relate specifically to the detector you are using.
A chart designed for another detector may be largely meaningless on yours.
Why Does the Target ID Keep Jumping Around?
A common question from new detectorists is why a Target ID appears stable from one direction but begins moving around when the target is approached from another.
There can be several reasons.
Target Depth
As a target gets deeper, the signal received by the detector generally becomes weaker.
With less target information available, identification may become less reliable.
You may therefore hear a faint but repeatable signal while the Target ID itself is less stable.
Depth can also combine with ground conditions to make identification more difficult.
This is one reason experienced detectorists don't necessarily ignore a target simply because the number on the screen isn't perfect.
Target Orientation
Objects underground rarely sit conveniently flat beneath the surface.
A coin lying flat can respond differently from the same coin standing almost vertically.
Irregularly shaped objects can vary even more depending on the angle from which the coil passes over them.
Turning through 90 degrees and sweeping over a target again can therefore provide useful additional information.
Nearby Metal
Several targets close together can make identification more difficult.
A non-ferrous object next to an iron nail, for example, may not produce the same response it would if it were sitting alone in clean ground.
The signals from nearby objects can influence what the detector sees beneath the coil.
This effect is commonly associated with target masking.
Modern detectors with faster target separation can help in contaminated ground, but tightly packed targets can still produce complicated signals.
Ground Mineralisation
The ground itself can affect target detection.
Iron-rich soils, wet salt and other forms of mineralisation can interfere with the detector's ability to clearly separate a target response from the ground response.
In heavily mineralised soil this can contribute to unstable signals, reduced depth and less reliable target identification.
Correct ground balancing and choosing an appropriate search mode can help, depending on the detector being used.
Target Size and Shape
Target ID isn't determined solely by what an object is made from.
Its size and shape also matter.
A large piece of metal may respond very differently from a tiny fragment made from the same material.
Thin, irregular or broken targets can also produce very different responses to a solid, uniform object.
Why Coins Don't Always Give the Same Target ID
Modern coins of the same type can often produce relatively consistent responses under controlled conditions.
Historical coins can be considerably less predictable.
Hammered coins are a good example.
They may be extremely thin, clipped, bent, broken or sitting at an unusual angle in the ground.
Their metal composition can also vary depending on denomination and period.
As a result, a small hammered silver coin may produce a considerably lower or less obvious response than a beginner might expect.
The same applies to many historical artefacts.
A target's age, rarity or value has no direct relationship with how impressive its Target ID will appear on the detector.
Something historically significant can produce a very ordinary-looking signal.
What About Gold?
Gold is another good reason not to become obsessed with numbers.
Gold targets can appear across a broad range of Target IDs depending on their size, purity, shape and alloy.
A very small gold item may produce a relatively low conductive response, placing it in a similar region to foil or other aluminium rubbish.
Larger gold objects may respond very differently.
This means there is no single “gold number”.
If you're searching for gold jewellery, rejecting every signal associated with foil or pull tabs can potentially mean rejecting gold as well.
Unfortunately, digging some unwanted targets is part of the process.
Target ID vs Audio – Which Is More Important?
The screen is useful, but don't forget your ears.
Your detector's audio response can provide information that a single Target ID number cannot.
As you become more familiar with your machine, you may begin noticing differences in the way signals sound – how sharp they are, how repeatable they are and how they behave when approached from different directions.
When investigating a signal, consider:
- Is it repeatable?
- Can you hear it from several directions?
- Is the tone clean or broken?
- Does the response disappear when you turn 90 degrees?
- Is the Target ID reasonably consistent?
- Does the signal behave differently when you shorten your sweep over the target?
None of those factors guarantees a good find, but together they can help build a better picture of what may be beneath the coil.
Should You Dig Low Target IDs?
Potentially, yes.
One of the easiest mistakes to make when starting out is assuming that lower numbers always represent rubbish.
Depending on the detector, small non-ferrous targets may appear relatively low on the Target ID scale.
This can include small gold items, thin hammered coins and small pieces of non-ferrous metal.
Unfortunately, foil and other unwanted targets can occupy similar ranges.
That overlap is unavoidable.
If you want to recover a wide range of potentially interesting targets, you will almost certainly dig some rubbish as well.
There is no discrimination setting that can perfectly separate every desirable target from every unwanted one.
Are High Target IDs Always Good?
No.
Higher conductive responses can include desirable coins and other non-ferrous targets, but large iron objects and unusual pieces of metal can sometimes produce convincing signals too.
Bent or irregular iron can be particularly troublesome.
Some iron targets can produce a non-ferrous response at the edge of the coil or from certain sweep directions.
The exact behaviour varies between detectors, sites and settings.
Again, this is why Target ID should be used alongside audio and signal consistency rather than in isolation.
Should You Dig Every Signal?
That depends on the site and what you're trying to achieve.
On relatively clean ground with good historical potential, you may decide to investigate most repeatable non-ferrous signals.
On a heavily contaminated site, digging every response may not be practical.
Your approach can also change depending on whether you're detecting pasture, cultivated land, woodland, a beach or a modern recreational area.
The important thing is understanding that discrimination is always a compromise.
Rejecting a range of targets can make a site easier to search, but it can also mean rejecting desirable objects that fall within the same response range.
Air Tests vs Targets in the Ground
Testing coins and other objects above the ground can be useful when learning a detector.
It lets you see how different objects respond and gives you a rough idea of where they appear on the Target ID scale.
But an air test is not the same as detecting a target in real soil.
In the ground, target depth, orientation, mineralisation and nearby metal can all affect identification.
So don't expect a coin buried at depth in difficult ground to necessarily produce exactly the same Target ID you saw when waving one beneath the coil at home.
Air testing is useful for learning the machine.
Real-world detecting is where you learn how that machine behaves under genuine conditions.
Build Your Own Target ID Knowledge
One of the best things you can do is learn your own detector rather than relying completely on charts found online.
Test a selection of everyday objects and coins.
Pay attention not only to the number displayed, but also to the audio response.
Then compare those results with actual buried targets when you're out detecting.
Over time you'll begin recognising patterns.
You'll learn which signals tend to be reliable, which types of target regularly fool your detector and which unusual signals are worth investigating.
That experience is far more valuable than memorising a long list of numbers.
Don't Chase Numbers – Learn the Signal
Target IDs are one of the most useful features found on modern metal detectors.
They provide another layer of information that can help you decide whether a target is worth investigating.
But they're exactly that – information.
They're not a guarantee.
Sometimes you'll see a perfect-looking number and dig a piece of rubbish.
Other times you'll investigate a weak or slightly uncertain response and uncover something that has been sitting beneath the ground for hundreds or even thousands of years.
Use Target ID alongside the detector's audio, the consistency of the signal and your knowledge of the site.
Most importantly, spend time learning how your own detector behaves.
The better you understand its language, the less you'll find yourself simply chasing numbers on the screen.