The OPSIS continuous emissions monitoring systems are the first in the world to be certified for extended gas calibration interval to 12 months. The recent tests show that our instruments are stable and keep very high quality. TÜV in Germany performed the long term drift tests, and the reports were finalized in June, 2015. Watch the OPSIS video about annual calibration. See the list of OPSIS QAL 1 certified instruments on QAL1.de. Please, contact us for more information.