one uses the weighted average rather than the median statistic to align the 6 spiral galaxies, then the SBF zeropoint changes by $-0.12$. Alternatively, if one chooses not to align the distance scales using individual galaxies at all, but instead using distances to groups of galaxies (Ferrarese [[et al. ]{}]{}2000), then this yields a change of $-0.13$ to the SBF zeropoint (Tonry [[et al. ]{}]{}2000). And finally, if one changes the SBF zeropoint by $+0.10$, then better agreement is obtained with predictions of population synthesis models (Jensen [[et al. ]{}]{}2003).[^2] Based on these considerations we assume that the systematic uncertainty on $\Delta_{\rm T01}$ is $\pm 0.13$ mag. This corresponds to an uncertainty $\Delta_{\rm II} = \pm 0.026$ in $\log(M/L)$.

After its calibration to agree with Cepheids, the SBF distance scale is subject to all the same absolute distance scale uncertainties that are inherent to the Cepheid distance scale. These are summarized in Section 8 and Table 14 of Freedman [[et al. ]{}]{}(2001). Most of the uncertainties affect both the distances of local galaxies, as well as the inferred value of $H_0$. They include: the distance to the LMC, the photometric zeropoint of the HST/WFPC2 used for the Cepheid studies, the 