The AQM4 is capable of taking four measurements in one instrument; carbon monoxide (CO), carbon dioxide (CO2), temperature, and relative humidity. Use calculated 8 hour Time Weighted Average (TWA) and 15 minute short term exposure limits (STEL) of CO2 for compliance testing and CO measurements for safety testing. Record, recall or download all readings to personal computer for later analysis or record keeping. The AQM4 is backed by a 2-Year limited warranty.