The SGGU-610/640 are designed to supply the zero and span gases required for calibrating an air pollution monitoring system.For the zero gas, atmospheric air is used as a raw material and purified to eliminate air pollutants. For the span gas, purified zero gas is used as the balance gas. The component gas contained in a canister is further diluted by the capillary type mixing method based on a ratio of flow rates. Thus, gas of a very low concentration, which is required for calibrating the air pollution monitoring system, is supplied.