The MM-100 Metabolic Monitor System measures oxygen consumption (VO2) and CO₂ production (VCO2) of small animals using the open circuit technique. The animal is placed in a closed chamber with a known flow of fresh air passing through it. Oxygen and carbon dioxide concentrations are measured at the inlet and outlet of the chamber. The three primary measurements (flow, O₂, and CO₂) enable the computation of oxygen consumption, CO₂ production,  Respiratory Exchange Ratio (RER), and heat production. Gas measurements are corrected for temperature and pressure.