Given that the diffusive motion of RBCs dominates the decay of $g1,MCtot(\tau )$, Eq. (15) thus stands as the quantitative relationship between the blood flow index measured by DCS and the true absolute blood flow. Recall that in order to get $BFi$, we first need to know the average optical properties of the tissue $\mu s,avg\u2032$ and $\mu a,avg$, which would generally be obtained from an independent NIRS measurement^{31}^{,}^{32} and possibly also estimated with multidistance DCS measurements.^{30} To then convert the $BFidif$ to $BFabs$, we need to know the proportionality $\alpha shear$ between shear flow and the RBC diffusion coefficient, the reduced scattering coefficient of the blood $\mu s,blood\u2032$, and the radius of the blood vessels. In this paper, we used a value of $\alpha shear=10\u22126\u2009\u2009mm2$ obtained from Goldsmith and Marlow.^{15} We note that this is a value obtained for a hematocrit of 40% to 47% and that $\alpha shear$ was found to linearly increase with hematocrit from 0% to 45% and then to plateau and reverse.^{33} The reduced scattering coefficient of blood $\mu s,blood\u2032$ is linearly proportional to hematocrit from 0% to 40%, the highest value measured by Meinke et al.^{21} In principle, if one has an independent measure of hematocrit, from a blood draw for instance, one can then determine the appropriate value to use for $\alpha shear$ and $\mu s,blood\u2032$. The remaining factor needed to estimate $BFabs$ is the vessel radius $R$. Although we performed simulations using vessels with a common radius, in reality DCS will measure vessels with a distribution of radii. We anticipate that Eq. (15) will still be valid when measuring a distribution of vessel radii, but that the effective vessel radius will represent a complex nonlinear dependence on the distribution of vessel radii and the corresponding RBC speed distribution.