Your post got me to thinking, I have also used Pro Zero on my AT Pro and on my AT Max with disc. at zero. So, I thought I would do some air testing in custom mode set up. This is my custom mode set up----disc set at 44, Sensitivity set midpoint, notch out 40, 45, 50 & 65, threshold 1. So, with these settings I was still able to get nice low tone on a silver ring, a gold ring, and a nickel. Mid tone on penny, high tone on clad dime, silver dime, clad quarter, and sliver quarter. I was pleased with the air test, especially getting a clear low tone on the rings and the nickel. I'm going this weekend to my daughter’s home in Mobile AL I plan to get a bit of detecting in I will report how my custom settings work I plan on doing some park hunting and possibly a little beach hunting. This custom setting is with the stock coil. For me the real test is in ground coins and relics the air test is a good refrence point.