Just about every metal detector manual that I’ve read (when the detector has a depth meter of some kind) says that the depth reading is a possible indication of depth for “coin sized objects”. Any thing smaller or larger under the coil can effect the accuracy of the depth reading. Target orientation is also a factor...
Excellent point, jmaclen...calibration to a coin sized target is a characteristic of all depth meters that I think a lot of folks tend to forget about. Manuals for other detectors I've owned have talked about the depth meter calibration in detail, but the Equinox manual is rather vague in comparison. But I think it's important to note that the Equinox might be calibrated to the approximate size of a US quarter. Page 35 of the Equinox manual says:
Minelab Equinox Manual, Depth Gauge, Page 35
Here is an example of the Depth Gauge reading and the approximate target depth for a US quarter detected in benign soil:
Minelab graphic showing one arrow for every two inches of depth for the quarter
Calibration to a quarter would explain some of the depth meter readings that I typically see on pennies and dimes (my most common coins), which often show 3 arrows (theoretically 6") but then turn up at 2.5-3" depth. The relatively small but shallow penny shows the same apparent size as a deeper quarter, so the Equinox assigns it a deeper depth. I don't find quarters nearly as often, but when I do, I often find that the depth gauge is pretty close to accurate. It all makes sense if you do the math - the surface area of a flat quarter is almost double that of a flat dime.
Anyway, once I realized all of this, I'm happier with the depth gauge on the EQ. In my head, when I get a penny or dime signal, one arrow equals 1" depth. A quarter signal, and one arrow equals 2" like the book says. If I suspect something other than a coin, all bets are off just like any other machine.
Perfect advice! Also lifting the coil progressively higher above the target while swinging will give you an idea of the depth on a coin,provided it’s not sitting weird as mentioned...
Absolutely, IDX! Lifting the coil a bit can provide a ton of useful information. If the target is "coin sized", and you lift the coil 2", the depth indication should increase by 2". If the target is noticeably larger than coin sized but deep, lifting the coil a couple or even a few inches won't impact the depth indication at all – you might even need to lift the coil half a foot or more before the depth indication changes on the really big stuff. Lifting the coil this way literally only takes an extra second or two, but will save you buckets of time compared to the long minutes you might otherwise spend digging 10" down just to recover a rusty, cell phone sized steel plate that rang up high and indicated 4" down. If the target is small and shallow, lifting the coil should cause too large of a change in corresponding depth indication.