It's called "How To-Is A PI Detector Right For You? .......The PI's Time Has Arrived To Take A Front Seat"
It has some mention of the history of metal detecting, the changes in the 60's and 70's in technology up to and including the most advanced PI technology with the ATX.
It has some mention of the history of metal detecting, the changes in the 60's and 70's in technology up to and including the most advanced PI technology with the ATX.