The GMD/W20 Series of CO2 transmitters are so stable, the company boasts that they require calibration only every five years. They feature the company’s silicon-based Carbocap® sensor that, according to the manufacturer, provides superior stability, accuracy, and temperature dependence over a broader temperature range. The measurement accuracy of the sensor is not affected by dust, water vapor, or most chemicals, it says. The Series measures carbon dioxide from 0 to 2,000 ppm, though they can be calibrated for other ranges. — Vaisala Inc. Woburn, MA