Gastecª Carbon Monoxide Gas Detector Tube features 3 pump strokes and 1/3 correction factor for 8 - 12.5 ppm measuring range, 2 pump strokes and 1/2 correction factor for 12.5 - 25 ppm measuring range, 1 pump strokes and 1 correction factor for 25 - 500 ppm measuring range and 1/2 pump strokes and 2 correction factor for 500 - 1000 ppm measuring range. Detector tube with sampling time of 2 min per pump stroke is ideal to detect carbon monoxide in air or the industrial areas and environmental atmospheric condition. Detector with 2 ppm detecting limit, changes color from yellow to blackish brown.