I've heard it been said on this forum that different brands of detectors will find things that other detectors missed or find things in " hunted out" sites.
I wonder if its not the detector itself or the "hunted out" site but rather that no one has ever swung over those particular targets before.
There are many many reasons a target is supposedly not seen by another machine. I can give you lots of them.
1. Frost heave. Targets move up and down in the ground just like rocks in a farmers field. One year he will have them all, the next many many more show up in plowing distance.
2. Moisture content. Most machines will reach deeper if the ground is wet. So on dryer days, a deep target might not register on any machine.
3. Orientation. BOTH the angle you go over the target and the angle it is positioned in the ground. You might go north to south one day and east to west another and find targets you didn't hit going north to south
4. Signal strength. Some machines can detect targets better and deeper than others. Companies KNOW that and price machines accordingly.
5. You actually missed it. Just because you KNOW you went over a particular piece of ground doesn't mean your coil didn't miss going over the target by even an inch. You have concentric coils and double D coils. At its deepest detecting depth a concentric puts a cone shaped signal in the ground and might only see a deep object in an inch wide window.
6. You decided to dig it. Everyone HATES zinc pennies. However a big fat gold ring and a gold coin will ring up with the same numbers as a zincoln. With a newer machine you just decided to dig the signal and got a huge surprise.
7. You actually do have a machine that will detect deeper than another you used. A possibility also. ALL machines are NOT created equal. You can have two of the same machine side by side and one will detect a target the other will miss. Nature of electronics
8. Target separation and recovery. Again you might also have a machine that can separate a coin from a nail close by and can pick them up separately instead of seeing everything under the coil as one object.
9. Some days you are in tune with your detector. Some days you can concentrate and really hear that faint signal. Other days too much is on your mind and you just are not in the groove.
AND last but not least!
10. You bought an Equinox and it not only finds things you missed, it finds things that were never there to begin with! It just made every other machine obsolete.
After Minelab catches up with demand, they need to make obsolete detecor recycling centers and give you a trade in allowance for your old CTX, Deus, and other pieces of trash so the landfills do not get filled up too fast.
I am sure others will chime in with more I missed. I have always sworn by my CZ's underwater. I got a Tiger Shark and was impressed with things I missed with the CZ's.
I am positive some of that was because I dug signals I got with the CZ's but decided not to dig and decided to dig them with the Tiger Shark.
I am also positive iron masked out targets with the CZ's and didn't with the Shark.
I took this from Big Boy's Hobbies page. In order to hit the deepest targets you have to move your coil less than an inch or two to hit all the ground that your detector can see.