At group meeting, Fadely showed us evidence that the radical self-calibration that we are executing for the HST WFC3 instrument can work: He showed that if you know the PSF—but nothing about any individual exposure—you can indeed infer the flat-field to some precision. Also and related, Vakili showed that he is getting pretty good estimates of the PSF in real HST WFC3 imaging. So we are getting close to going end-to-end on this project. I call this self-calibration “radical” because it doesn't rely on stars being observed more than once; it only relies on stable enough (or dense enough) imaging that the PSF can be accurately inferred. It works by asking what flat-field is required in order to generate good predictions for the data. One thing we are hoping: The quality of the results might depend more on the center of the PSF (the easy part) than the outskirts (the hard part); we are trying to understand that now. The long-term goal of this project is to save the asses of projects that took their data in violation of the principles for self-calibration.