The CO2 Tester Kit by Control Wizard allows for accurate testing of CO2 levels. Includes 2 tubes (2 tests). Draw 100 cc's of your growing area's air into the syringe. Break off both ends of a glass reagent tube and insert the tube into the syringe with the arrow on the tube pointing away from the syringe. Now gently push all the captured air through the tube. Now examine the tube. Where the purple color stops and the white begins is a PPM number. That's the CO2 count in your area.