I have mine and I used this tester 2 years back and it has been in storage, I am sure things are tweaked on this unit and they made it better, I have new marine kit that I got in the mail but my unit was giving me problem, I have sent it back to them so that it could be looked at, I like the idea and I can reach them on the phone and person on the company side was very informative and communication was great, I am waiting for my unit to be sent back, hopefully I will be able start testing again with this unit, I agree with gus6464 getting correct results out of any test kit is to follow instructions from manufacturer and not doing so is going to cause inconsistent results and confusion.. I will be posting my results when I get my unit back, I will compare the results with Elos brand new kits that I bought due to this tester being down, I am sure it happened for good reason...