ABL-4021 AutoCal® Respiratory Air Monitor The ABL-4021 is designed to continuously monitor for the presence of carbon monoxide in compressed breathing air. The CO concentration is displayed on an illuminated digital readout with a range of 0 to 100ppm. The flow rate is displayed on a flow meter. When threshold values are exceeded, a warning alarm is activated and a low flow message appears on the display. The ABL-4021 is supplied with a standard 110V AC line cord but may also operate on 12V DC. Automatic recalibration is accomplished without having to adjust a control.