The Barten Ramp is calculated from P. G. J. Barten’s 1999 Contrast Sensitivity Function (CSF), a model that supposedly incorporated most of the important variables in the ability of the HVS to detect contouring in digital display systems. Note this is modeled rather than measured data and the model is based on data that predates the 1999 model. Measured data from W. F. Schreiber’s 1992 book shows the eye is not nearly as sensitive to contrast steps as Barten’s CSF model indicates… While a 10 bit version of the PQ EOTF would exceed the threshold based on the Barten CSF model, it would stay well below the threshold established by Schreiber’s measured data. The satisfactory application of the 10 bit PQ function by HDR10 supporters would seem to indicate that Barten sets too strict a limit. For example, at 1 nit of luminance, Barten says the HVS can detect a 0.5% brightness step but Schreiber says the HVS can only detect a 2.0% brightness step. This is a huge difference. Which is right?