I bought one of the Biologic probes a few years ago.. seems like it pretty much reads the same no matter what soil I put it into. I did, however, stick it into a tomato once to see what it would do and it went to very acidic like I had expected.. So I guess you could say it works to some extent if you're looking for extremes, but If you are trying to refine your soil you better get one of the test kits from one of the places mentioned or from your local ISU extension office.