Product review (5 stars): This little gem right here.
Excellent quality, works flawlessly and is easy to use. No instructions necessary. I've been using it in my garden for 5 months now and it has had no issues at all. I enrich my garden atmosphere co2 from the normal 350ppm to around 1200ppm. Sometimes I treat for pests by flooding with co2 and this meter has an alarm you can set from 0 to 9999 ppm. I open a tank of co2 and walk out the door, I only return after the alarm has turned off (i keep it set to alarm at 5000 ppm and alarm turns off once it gets below 2000ppm.)