I'm pretty sure I received a defective unit. It didn't work properly at all. I've used many leak testers before and I followed the directions with this one so I'm sure I was using it correctly. Regardless, it didn't work. I returned it and got my money back. I wish I had a working device to properly test and give a better review but it is. Packaged very well and looked like a quality product but I think it was partially clogged resulting in extremely inaccurate readings.