Just got my F70 today and tested it on some test coins. I was able to get some impressive depth out of it. the secret seems to be the right mixture from Disc, speed (De or slow), threshold and sensitivity. The threshold seems to have a very huge impact on stability and depth. The slow setting picks up more disturbance from power lines than the de setting. The slow speed also has much more punch than the de speed and the target feels much larger. Kind like the JE mode on the F75.
I used the F70 in de speed, disc at 0, threshold at 0 and sensitivity at 70. The auto tune all metal mode has some scary depth.
I checked the slow speed and even at low sensitivity setting the depth was very good. Even at sensitivity at 1 (one) it did still airtest a coin at 8" in slow. The sensitivity numbers are not linear, a setting of 99 does not give you 99 x 8 inches. It seems like at sens one the detector is at about 60 % depth in slow speed.
For those who may run into instability problems under power lines: Set the threshold lower than - 3.
These are my impressions after playing with it for a few hours and it is not written in stone.
That's it for now....more later....
Andy,NM