Dunno if I'm unlucky but mine test is not woth a clue. He shows me on long range a value of 24. I couldn't believe when I went to my shop and the seller showed me 1ppt No3.I came back home with jbl test kit and I had 1ppt on it too! So I tested again and again with the rsm test kit - all time not real reading. The expiry date on the package is 04.2017. I will try it again but 1 star from me today.