The GMD/W20 Series of CO2transmitters are extremely stable, requiring calibration only every five years, the company says. They feature the silicon-based Carbocap® sensor that provides stability and accuracy over a wide temperature range; measurement accuracy is not affected by dust, water vapor, or most chemicals, says the company. No add-on software or external software compensation is needed. The units measure carbon dioxide from 0 to 2,000 ppm, but they can be calibrated for other ranges.

Vaisala Inc., 100 Commerce Way, Woburn, MA 01801; 781-933-4500; 781-933-8029 (fax); (e-mail).