The PPM-1c is an extremely accurate CO2 sensor. It measures the exact level of CO2 in your growing area and displays this value from 0 to 5000 Parts-Per-Million (PPM) on its' digital readout. Even though the PPM-1c can be used as a simple way to measure your CO2 level, the true potential of the PPM-1c is not realized until it is connected to one of the controllers C.A.P. has designed to work with it. When the PPM-1c is connected to either the CO2-2e , CO2-4e or CGC-1e, it commands the controllers to release or produce more CO2 only when required. The timers built into the atmosphere controllers continue to coordinate with the PPM-1c to give you the precision control not possible with other manufacturers CO2 control systems using only ON/OFF control. You enter the exact level of CO2 you want to maintain (usually 1500 PPM) and you're done.