Fig. 2. Bias for the three oximeters is plotted  versus oxyhemoglobin saturation, Sao², measured by a Radiometer OSM-3 multiwavelength oximeter (hemoximeter). Bias is calculated as Spo²(oximeter measured value of oxyhemoglobin saturation) minus Sao². Light-skinned subjects are indicated by  open circles , dark-skinned subjects by  closed circles . (  A ) Nonin Onyx, (  B ) Novametrix 513, (  C ) Nellcor N-595. Linear regressions were performed separately for light-skinned and dark-skinned subjects and are statistically significant (  P < 0.001). Multivariate analysis showed statistically significant effects for both skin pigment and oxyhemoglobin saturation (  P < 0.01).