C.A.P. (Custom Automated Products) PPM4 C.A.P PPM-4 CO2 Monitor Controller Carbon Dioxide Hydroponics PPM4 CAP Sensor Monitor and control co2 dispersal throughout the growing area Highly visible and intuitive LED indicator display to let you know generalized co2 levels at a glance from across the room Easy to use calibration function 0-900 PPM product 901-1450 ppm