Positioning a medical device based on oxygen saturation measurements

A method that includes receiving first and second detection signals and electrocardiograph signals; wherein the first detection signals result from an illumination, by an oxygen saturation sensor included in a device that may be removably attached to a user, of a sternal angle of a user by infrared pulses; wherein the second detection signals result from an illumination, by the oxygen saturation sensor, of the sternal angle of a user by visible light pulses; wherein the electrocardiograph signals may be detected by an electrocardiography sensor that may be included in the device; generating a first waveform template that may be responsive to the first detection signals; generating a second waveform template that may be responsive to the second detection signals; calculating an indication of the oxygen saturation characteristic of the user in response to the first and second detection signals; detecting cardiac cycle durations that may be based upon the first and second detection signals; detecting electrocardiography based cardiac cycle durations; and evaluating a quality of the indication of the oxygen saturation characteristic of the user in response to the first waveform template, the second waveform template, the cardiac cycle's durations and the electrocardiography based cardiac cycle durations.