When calibration was done, it was generally done manually. Even facilities with automatic calibration functions on their CEMS typically conduct manual calibrations because they can bypass the sampling system. This reduces the amount of calibration gas used, thereby reducing costs. However, by only calibrating the analyzer, any problem in the sampling and conditioning system will not be discovered. One local EMC reported that many facilities relied on the EMC’s reference tests (typically conducted one to four times per year) to calibrate the CEMS. In other words, those facilities do not calibrate their CEMS on a regular basis as required. HJ/T 75 expressly prohibits using the EMC’s reference test as the basis for calibration or the relative accuracy tests required every six months.