What has the AML Pro got in common with a Ouija board?
It does not work. The physics says it cannot work. That part has been settled for a while. The harder question is the one I get asked on every course: then why do people come back from site saying it found the pipe? The answer is not in my opinion. It is printed in the manufacturer’s own operating instructions.
A Ouija board works. Nobody disputes that the planchette moves. What is in dispute is what moves it.
That is the whole of this page. The AML Pro has real electronics inside it, and its lights really do come on. The question is what turns them on, and whether the person holding it can tell the difference.
1Start with the settled part
None of this is the interesting bit any more, so it gets four lines and a link.
- The frequency is wrong for the job. Every real ground penetrating radar built for utility depths works between roughly 200 MHz and 1,500 MHz. Higher frequency buys resolution and loses depth. The AML Pro transmits at 2.45 GHz.
- 2.45 GHz is the frequency water absorbs. It is the microwave oven band, chosen because water soaks it up. Wet ground is the condition the device is advertised for.
- The power is tiny. Their own laboratory measured 41 mW when the unit was certified. That is roughly what a wireless keyboard is permitted. The full working is here.
- Fourteen years, no blinded test. Not one demonstration, by anybody, of the device locating an unknown target above chance.
The physics case is made in full in the long investigation. This page assumes it and moves on.
2So why does anyone believe it?
Because the people who come back saying it worked are not lying, and they are not stupid. They are experienced locators describing what they honestly saw. Something moved. Two lights came on.
The effect has a name and it is over a century old. It is called the ideomotor effect: a small, genuine muscular movement produced by expectation, below the level at which the person notices making it. It is the accepted explanation for the Ouija planchette, for dowsing rods, and for facilitated communication.
The ideomotor effect needs three things to produce a convincing result. An expectation of where the answer should be. A freedom of movement fine enough that small corrections are invisible to the person making them. And no feedback that can contradict them.
Hold that list. The rest of this page is about how well the AML Pro’s prescribed operating technique satisfies all three.
3The instruction that gives the game away
This is from SubSurface Instruments’ own operator’s manual for the AML, the edition printed while the patents were still pending, so before 2011. It is on the page headed How it works.
Read what that instructs. The device has given you one light. You believe there is a pipe. So you are told to move your hand until the second light agrees with you.
That is not a locating procedure. That is the operator being appointed as the source of the answer, and the instrument being adjusted until it confirms them. It is the mechanism of a Ouija board, written down as a step.
Dated deliberately. I checked this against every manual we hold: the 2014 multi language edition, the 2015 revision, the V4.29 of February 2021 that came in the box with our unit, and the current V4301. That instruction is in none of them. It was removed. I am not going to pretend it is current text, because it does not need to be. It tells you what the device was designed around.
4The same manual, on what to point it at
Two pages later, under Technology Overview, the manual explains when the AML is most useful. I have added no emphasis. This is how it is printed.
The recommended use case is a utility the operator already knows is there. That is the expectation, supplied by the manufacturer.
And on the same page, on the question anyone technical would ask first:
The same paragraph adds that the locator “cannot tell you what the target is; that’s up to you”, and that “you just have to know, or figure out, what you are on”.
And on the searching page, on confirming a find:
Your desired target. Is this reasonable. The test of whether a reading is real is whether it matches what the operator wanted and expected to find. There is no other test offered.
5Now the current manual, and the freedom of movement
Expectation was the first condition. The second is enough freedom of movement that small corrections go unnoticed. This part is not historical. It is the manual SubSurface Instruments ship today, pages 18 to 21.
This is SSI’s own diagram of it, from page 20 of the manual that came in the box. Note what the two little figures are doing, and note the gap the diagram itself draws between Laser Mark and Actual Location.
The prescribed technique moves the instrument through three angles:
| Stage | Angle | What the manual instructs |
|---|---|---|
| Searching | 10° | Blade projects 10° outward, handle parallel to the ground, 18 inches in front of the body, swept in a back and forth W. |
| Locating | 0° | Once something is found, pivot the handle upward until the screen reads 0° and the blade sits over the signal. |
| Depth | 45° | Tilt the handle down to 45° and walk backwards until you detect the top of the pipe again. |
On top of that, the indicator itself is motion dependent, and the manufacturer says by how much. From their own published FAQ:
“Both lights will come on then go off approximately every 2 inches when the antennas are located inside of these null zones. A gentle flicker up and down or a vertical motion will allow the pipe to be accurately re-located.”
2.45 GHz has a wavelength of 12.24 cm. Half of that is 6.1 cm, which is 2.4 inches. The indicator is cycling on and off with roughly every half wavelength of hand movement. So a person holding it has a light that changes state every couple of inches, in three taught angles, at 18 inches of reach, swept in a W.
You do not have to take my word for the two inches. It is one of the questions SubSurface Instruments answer on their own FAQ page, and it is worth reading the list of questions they thought needed answering.
Read the tenth question again. “When on the edge of a pipe, why do I lose signal just by raising or lowering the AML by an inch or two?” An inch or two. Raising and lowering is not a different kind of movement from sweeping. It is the same antenna, moved through the same half wavelength.
And then there is the strangest instruction of the lot
Back on the searching page of the old manual, at the end of the paragraph about confirming a find, is this:
“When detecting, move the unit, not your feet.”SSI AML Operator’s Manual, “Patents Pending” edition, page 10
Sit with that for a second, because it is the sentence that finished this off for me.
An instrument that reads the ground cares about one thing: where its antenna is. Not how it got there. Move the unit six inches to the left, or keep the unit still and take a small step to the left, and the antenna ends up in the same place over the same ground. A device measuring what is buried below would return the same answer either way, because physically it is the same measurement.
So why would it matter which one moved? It only matters if what is being measured is not the ground.
The two are not the same for the person holding it. A hand movement is fine, continuous, and small enough to go unnoticed by the person making it. A step is coarse, deliberate and conscious. If you want an indicator to settle where somebody expects it to settle, you want the first kind of movement and not the second.
I am not claiming that is why the line was written. I am pointing out that for a working locator the instruction is meaningless, and for the effect described in section 2 it is exactly the right advice.
6And no feedback that can say no
The third condition. For expectation to be corrected, something has to be able to contradict it. Here is what the current manual offers instead, in its own words.
- “The proper operation of the AML Pro requires a lot of practice. We advise that you practice on a known buried object like a culvert pipe or other partially exposed objects.”
- “Do not hold the unit above the handle finger knurls as it will produce false readings.”
- “Lower the sensitivity level to the lowest setting that will still identify the object; this will prevent most false readings from being identified.”
- “Factory training is available and highly recommended.”
Look at the third one. On a device whose entire output is something is there or nothing is there, the operator is told to turn the sensitivity down by hand until the readings they do not want stop appearing.
Put together, the architecture is closed. A hit that matches expectation is the device working. A hit that does not is a false reading, and there are instructions for making those go away. A miss is not enough practice. Nothing that happens on site can come back as evidence against the instrument.
7Which brings us to the videos
People send me demonstration videos as if they settle it. Watch the next one you are sent and ask a single question: did they already know where that pipe was?
- Tracing along an obvious trench line, on ground that was dug and reinstated.
- Walking from one valve box towards the next one, both visible.
- Following a line already marked on the surface.
- A pipe on the demonstrator’s own test plot, buried by the demonstrator.
None of those tests the device. Every one of them supplies the answer before the walk starts, which is exactly the use case the manual recommends.
What would settle it, in an afternoon. Somebody buries a length of plastic pipe in ground the operator has never seen. The operator is not told whether anything is buried at all. They mark where they say it runs. Then it is dug. Repeat enough times that luck cannot explain the score. That is a blinded trial. In fourteen years on sale, nobody has published one.
8Why this one matters more than the physics
You can argue about wavelengths for a long time and most people on site will reasonably say they are not physicists. Nobody needs to be a physicist to follow this one.
A device that tells you to move your hand until it agrees with you is not measuring the ground. It is measuring you.
And the decision being made with it is where to put a digger. That is the reason I keep writing about this rather than letting it go.
The long investigation has the physics, the patent record and the industry context in full. The five minute version is the one to send somebody who is about to buy one. The power figure covers the specification that has never been published.