I am more of a colored stone guy and my customer relation skills are a bit rusty. What I did learn about Diamonds was out of self defense. If some one dose bring me a diamond ring I send them to the pawn shop I know the guy I have seen him check lots of rings and I am sure he has done this a thousand times. With that said he has at least two testers that I have seen, and cleans and drys every thing, works in a store with a good air conditioner, he knows how and way the tester works and yes I have seen him use both testers on the same stone. My dad had a saying PFM pure f@%# magic , he was a test pilot and had to fly plains with black boxes in them that no one would tell him what was in it or what it did PFM, to say he disliked this is a gross understatement. After one of these PFM black boxes nearly killed him, they started to tell him at least what the box was suppose to do, the project was a success…If you have a black box dont just do the “magic” learn what its supposed to do and how it dose it if you can. Ps Thanks Trevor I know you get it. now i just need to figure out my new PFM phone