Fig. 3. Pooled pulse oximeter oxygen saturation (Spo2) reading observations by digit and forehead sensors in supine (0°) and two Trendelenburg positions (−10° and −15°), with headband usage at the lower ( A ) and higher ( B ) tension settings. Subjects breathed room air throughout the study. Each subject’s average readings under the tested conditions are indicated by the large points connected by lines , overlaying the individual sampled observations ( small open points ). Digit sensor saturation readings are shown at the left ( white points ). First, second, and third forehead sensor data groups at each angle indicate, respectively, the saturation readings with the headband placed before tilting the subjects (HB1; dark gray ), upon removing the headband (W/OHB; light gray ), and after headband reapplication (HB2; dark gray ). Best forehead sensor performance occurs when the headband is used and is placed before tilting the subjects.