I have been traveling for the last two days, hence the lack of posts. I re-learned how to do SDSS CAS queries, to obtain a complete list of the science-grade images used to construct SDSS DR5. We are running astrometry.net on all of them to measure statistics (and build knowledge of the sky, of course). I also worked on various strategies for tweak. I have a very robust one (though it is still vapor-ware) that iteratively fits not the WCS mapping, but the residuals in the current best-fit mapping, and iterates until the residuals have no power at the scales at which we are fitting.