The relative influences of the absolute mean value error, the confidence interval value, and the instrument calibration accuracy is examined using on-site instrument certification data acquired in the past three years. Confidence interval has strong influence based on existing certification data. The trend emphasizes the importance of the sampling technique. Properly calibrated instruments provide low values of absolute mean value error. An induced error related to calibrating instruments to 1.5 times the applicable emission standard for full scale has been observed when the relative mean value (reference average of sampling values) is low. The effect of the induced error will be amplified when the instrument calibration is performed improperly. Extractive emission monitoring systems using ultraviolet visible absorption detection techniques have successfully met the performance criteria proposed by the Environmental Protection Agency based on evaluations conducted in power plants, nitric acid plants, and sulfuric acid plants.