The PG-300 is a compact and lightweight stack gas analyser that can simultaneously and precisely measure up to five separate gas components with reference methods. NOx is measured by Cross-flow modulation chemiluminescence detection method, the SO2, CO, and CH4 use a Cross-flow modulation Non-dispersive infrared (NDIR) absorption method, CO2 module uses standard Non-dispersive infrared (NDIR) absorption method, and the O2 unit uses zirconia method, galvanic method, or paramagnetic method.