Following Pauling's success with the development and construction of an effective oxygen meter, the OSRD assigned him and his right hand man, James Holmes Sturdivant, to serve as official investigators in the development of a carbon monoxide (CO) meter. The meter was intended to measure the levels of carbon monoxide in the air. CO, a colorless, odorless, and tasteless gas, bonds to hemoglobin in the human bloodstream. In the process, carboxyhemoglobin (also known as carbonmonoxyhemoglobin) is created, preventing delivery of oxygen to body tissue, eventually resulting in brain damage and death.

In high temperature environments where there exists an abundance of carbon, the combustion of carbon releases nitrogen and carbon monoxide. In some tank cabins and airplane cockpits, CO could be released by the repeated firing of the vehicle's weapons systems. This gas would then build up in the compartment occupied by the crew, sometimes leading to poisoning. As a result, the U.S. military desired a means of quickly testing carbon monoxide levels, which would allow for preventative measures to be taken before loss of life occurred.

The men quickly realized that traditional chemical indicators like iodine simply weren't well suited to this apparatus' requirements. After only a few days of research, they discussed the possibility of using an organic substance as an indicator - hemoglobin seemed a likely candidate. After some calculations and a small amount of experimentation, the men were ready to build a prototype.

The apparatus contained a sample of hemoglobin molecules bonded with oxygen, otherwise known as oxyhemoglobin. When this sample came into contact with carbon monoxide, carboxyhemoglobin was created. The sample was then measured by a spectrophotometer - one of the DU models that had made A. O. Beckman famous - providing the user with a reading of carbon monoxide parts per million in the immediate vicinity. Because the conversion of oxyhemoglobin to carboxyhemoglobin was reversible, the apparatus could take consecutive readings without maintenance.

They quickly found it more difficult than expected to build a working spectrometer that could accurately read carboxyhemoglobin levels. Between October 1942 and November 1943, Pauling and Sturdivant built several spectrometers, attempting to calibrate them in such a way that other environmental changes such as the addition of pure oxygen would not disrupt the readings. Finally, in December of 1943, they had taken the project as far as possible.