Abstract: The invention relates to a non-invasive oximetry process for determining the value of oxygen saturation of the blood of a subject. In some ear oximetry processes, light at two or more frequencies is transmitted through the ear lobe or pinna of the ear of a subject, and the intensity of the transmitted light is measured on the other side of the ear lobe. These processes are affected by such variables as depth of blood in the ear lobe or pinna and differences in the total hemoglobin concentration in the blood. Applicant has discovered that inaccuracies caused by these variables can be eliminated or greatly reduced by taking the derivative of the intensity of the transmitted light, and processing the values of these derivatives in association with a set of predetermined pseudo coefficients by applying these to newly developed relationships disclosed in the specification. The result of such processing yields the value of oxygen saturation of the blood of the subject.