1. Sensing resistance in air R 0 is measured under controlled ambient conditions, i.e. synthetic air at 23 ?5?C and 50 ? 10% RH for RED sensor and synthetic air at 23 ?5?C and ≤ 5% RH for OX sensor. Sampling test. 2. Sensitivity factor is defined as Rs in air divided by Rs at 60 ppm CO. Test conditions are 23 ? 5?C and 50 ? 10% RH. Indicative values only. Sampling test. 3. Sensitivity factor is defined as Rs at 0.25 ppm NO 2 , divided by Rs in air. Test conditions are 23 ? 5?C and ≤ 5% RH . Indicative values only. Sampling test. 4. Sensitivity factor is defined as Rs in air divided by Rs at 1 ppm of NH 3 . Test conditions are 23 ? 5?C and 50 ? 10% RH. Indicative values only. Sampling test.