I did a lot of research on the two a while back before i bought my 3d. Here is the thing. If both detectors are properly tuned, they should get the same depth. What has been happening (i read this on Tom Dankowski's forum) is that some batches of new CZ 3ds have not been well tuned, so there are more inconsistencies between different CZ3D detectors unit to unit. Some are hot and will pick up a dime at 12'' others can only hit a dime at 8'', the average is about 10'' for a dime. According to Tom, CZ70 has less inconsistencies model to model (maybe due to the digital aspect), so on average you are more likely to buy a properly tuned CZ70 which might go deeper than your average CZ3D.
This is really a shame because i think the 3D is a better machine, i my opinion, the analog model can be adjusted better to the conditions on the ground. The only benefit of the digital model is notching, but unless you are in an area where there is a particular pesky trash item that is very common, notching is not that useful. I never use it on my 7a, although i used to use it on my Garrett back in the day. That's because there are many more notches on a Garrett, on a digital CZ there are only 7 segments, while the high end Garrett models have 24 segments and even the bottom of the line GTX's 350, 400, 550 etc.. have 12 segments (24 for 550). So with Fisher, if you to decide and notch a segment, it eliminates a much wider range of items that could potentially be valuable. I also don't like that the items on the digital scale are not listed in the order of conductivity. That's why when the target is between segments due to corrosion, there is jumping from one segment to another, which usually skips a segment. You can memorize the correct order, but i found it confusing.
I am not saying that the digital CZ's are bad machines, i think they are great machines and are very easy to use. My CZ 7a is spot on when it comes to identifying coins at depth with a smooth solid signal, which i can't say for some of the Garretts i have used where the segment meter would jump around constantly (that's because there are more conductivity segments to jump between and a greater chance of the target being between segments). I just think that the digital CZ's don't have much to offer over the analog CZ's, in that they don't have any special programs like the V3, Etrac, Explorer, GTI 2500, MXT's and XLT's or the F series which can be readily accessed with a push of a button and allow for an even greater tuning of the machine to the conditions on the ground.
I guess the final question is whether the machine you are getting is properly tuned, if you can air test the CZ70 you're getting, and it hits a dime at 12'', i would grab it because the odds are the CZ3D you will buy probably won't (although you never know). I see people on here buying and reselling their machines in hopes of coming across a hot one, but it's hard to find a second hand machine that is hot because people are not going to sell it. If you can get your hands on a CZ3D that can hit a dime at 12'' i would never sell it (assuming that it's stable and the identification part works correctly). There are times when those few extra inches will make a big difference
Here is the link to the CZ70 vs 3D topic on Toms website:
http://www.dankowskidetectors.com/discussions/read.php?2,1454,1463#msg-1463
Good luck!!! and happy hunting!
