A triaxial alveolar gas diagram to depict fractional concentration of
oxygen, carbon dioxide and nitrogen is described, in which the R = 1 l
ine is always implicit. Although it is not claimed that this represent
ation leads to new insights into respiratory physiology, a method of p
lotting on a triaxial coordinate system has been found to be well suit
ed to many applications when a direct display of fractional nitrogen c
oncentration is required.