Figure 3. Plot of the error (cerebral oximeter reading [rSO2]-measured jugular bulb venous saturation [Sjvwith bar O2]) versus the mean of rSO2and measured Sjvwith bar O2using the method of Bland and Altman [24]for both experiments and all test stages for all 30 volunteers. The plot indicates that the cerebral oximeter reading and the standard measure are not closely associated because the limits of agreement are wide. Precision was defined as 2 SDs about the mean error (the bias). Open symbols = data for normocapnic experiments. Closed symbols = data for hypercapnic experiments. Triangles = data for three volunteers with large negative error for all measurements.