Does anyone here know what the ATX is actually measuring when it generates low-high and high-low tones? Since it is a PI machine and operates on a completely different principle from VLF machines, I'm wondering what it is measuring to generate these tones (Conductivity? Magnetic susceptibility?) How is it getting this info out of a pulse (not VLF) return? Is it looking at response time lag/decay time? Return pulse spreading? Some kind of return frequency content/Fourier analysis?