A portable alveolar gas measurement device and method of determining at least one alveolar gas level are disclosed. The device includes a structure that receives a sample portion of breath, and a gas sensor in communication with the structure that detects a gas level of a gas within the sample portion and provides a first signal indicative of the level. The device further includes circuitry coupled at least indirectly to the gas sensor, where the circuitry receives at least one of the first signal and a second signal related to the first signal, and where the circuitry provides at least some assistance in determining whether a portion of information provided by the at least one signal is used as an indication of an alveolar gas level. Additionally, the device includes an output device coupled to the circuitry that provides an output indicative of the first alveolar gas level.
