Depending on depth and moisture content, silver dimes on the SL90 are '82-3, clad dimes are 79-81, memorials are 77-8, and wheats are 74-6....at least on my machine....and 2 of my friend's machines. Now I'm sure you can find some alkaline cesspool or other bad ground somewhere where they'll all sound the same but in the areas I've hunted these are the numbers I get, down to the 8" level. In favorable ground, like dry beach sand, they'll be accurate even deeper. The E-trac says 12-44 for all of them, but will do so at deeper levels, so I can live with that! The Explorer I used had similar results. Of the modern machines, the CTX is the most impressive to me. I've borrowed a couple from friends, so I'm not a 100 hour veteran yet but I do have hundreds of hours on the E-trac which has the same numbering system and similar features. It doesn't do much better on exact TID but it does so at impressive depths....especially with that 17" coil. If I knew a 12-44 was a memorial, I might pass it by if it was necessary to cut a plug, but I would scoop it at the beach. If it was deep enough in an old park, I'd still dig it as it might be something good. I dug the '77-8's with my SL90 too, even though it was almost a certainty that it was a memorial. I've found a few silver rings, other jewelry, and wheats/mercs with those numbers from time to time that would try to fool you. Until they come up with a detector that will give you a digital photo of the target before you dig, it's just best to dig anything close to a good TID if you don't want to miss something good. You just need to weigh the likely outcome vs. the effort involved. To get back to the OP's question, I'd get a machine that goes deep if that is where the good targets are, regardless of how accurate the TID is. If you have it set correctly, and your hearing is ok, you'll eventually learn what to dig and what to pass by even if the numbers are iffy.
