This controller works awesome..... At first I got screwed up cause my breath was messing up the readings. I left it alone for a while and let it work, and when I came back the levels were just about where I set them, 1500ppm.One thing that takes some time to dial in was the flow rate on the co2. Start with ur flow rate very low and see how quickly the levels increase in your room, as well as the overshoot histeresis. If you are flying by your set point by more than 50ppm, you're flow rate is too high. You don't want to waste it, so take the time to adjust it.also, make sure u have good air flow around the controller, its very important. I mounted a pc fan directly under vents blowing up through the unit. This way it has a good air sample to work with.Calibrate the unit outside, it works much better....just run an extension cord outside and leave it alone, if u stand near it, u will screw it up.....takes about 20 minutes.Good luck!