Pinpointing is mostly muscle memory. This guide covers general technique, the specifics of the ACE 400’s stock DD coil, and a practice plan to build accuracy.

How the DD coil “sees”

DD coil detection field: top view, plus front and side views of the field

The ACE 400’s stock 7”×10” PROformance coil is a Double-D (DD) design. Two D-shaped windings, one transmit and one receive, sit back to back with an overlap. The overlap produces an elliptical sensing zone that runs toe to heel and gives a chisel-shaped signal that covers ground evenly.

  • Across the sweep (left-right): the field is a narrow wedge. The peak is sharp, so left-right pinpointing is accurate.
  • Toe to heel (front-back): the field is a long chisel. The peak is vague, so front-back location is less precise.
  • Once centered, the target is usually under the middle of the coil, roughly below the shaft mount. Verify this in your own test garden.

DD coil pros and cons

  Detail
Harder pinpointing DD coils need a deliberate technique, and larger DD coils are harder to pinpoint. A smaller DD (about 5×8”) pinpoints much tighter than the stock 7×10.
Near obstacles The elliptical housing puts the sensing area close to the edge, so you can hunt beside trees and fences if you sweep parallel to the obstacle.
Ground mineralization A DD sees about 70% less ground mineral effect than concentric coils. It runs more stably in mineralized or shifting soil.
Coverage Scans a wider path and needs less strict overlap. Overlap still matters at the depth limit, where the field narrows.
Frequency Coil performance depends on operating frequency. The ACE 400 runs single-frequency at 10 kHz, which is good for coins and relics and weaker on tiny gold.

Core technique: the X (crosshair)

  1. Sweep side to side until the tone peaks. Note the spot.
  2. Turn 90° and sweep across that spot. With a DD coil this matters most, because the second pass crosses the long strip the other way.
  3. Repeat with shorter, slower sweeps until the strongest signal is under one spot. Keep the coil flat and at a steady height the whole time.

ACE 400 pinpoint button

  • Non-motion mode: hold the button and the coil can hover. The tone rises in pitch and volume as you get closer to the target.
  • Start off to the side: press it with the coil to the side and a few inches up, then keep holding as you slide over the target. Pressing directly over the target cancels it out.
  • Detune to narrow it: over a strong signal, release, then press again with the coil partly over the target. Repeat 1–2 times and the hot zone shrinks to a couple inches. This is the best trick for big or shallow targets.
  • All-metal: pinpoint mode has no discrimination, so a nearby nail will pull the signal. If the pinpoint center doesn’t match where the discriminating sweep peaked, suspect iron next to the target.
  • Depth reading: the display shows depth in 2” steps. It’s calibrated for a coin-sized target, so large objects read shallower than they are and tiny ones read deeper.
  • Iron Audio: turn it on so iron gives a low grunt even when it’s notched out. This keeps you from passing over a coin that sits next to a nail.

Other techniques

  • Wiggle: small 2–3” side-to-side motions over the spot sharpen the signal.
  • Edge pinpointing: use the coil’s tip or tilt one side up for a narrower field.
  • Lift test: raise the coil slowly. A small or deep target drops out fast, and a big shallow one keeps signaling.

Practice plan

When Drill Goal
Week 1 Air test. Lay a coin on a table and use pinpoint to find the coil’s true hot spot. Mark it on top of the coil with tape. Know your sweet spot
Weeks 2–4 Test garden. Bury a coin, nail, pull tab, ring, and bottle cap at 2”, 4”, 6”, and 8”, about 2 ft apart, and map them. Let the soil settle a few weeks. Learn signals by depth
Weeks 2–4 Blind drill. Have someone bury a coin. Pinpoint it, push in a golf tee at your center, dig, and measure your error. Log every attempt. Error under 1”
Ongoing Plug check. Check the plug and the hole separately before digging further. Find any consistent bias
After that Coin plus nail. Bury pairs 2–4” apart and practice separating them. Handle trashy ground

Common errors

  • Coil height changing during the sweep, which shifts the peak
  • Sweeping too fast near the target
  • Pressing pinpoint directly over the target
  • Assuming the DD hot spot is a point rather than a toe-to-heel strip

Gear

A handheld pinpointer finishes the job once the coil has you within a few inches. It roughly halves dig time and hole size. The Garrett Pro-Pointer AT pairs naturally with the ACE 400, and the Carrot is a budget option.

Further reading