is it possible to know how wrong your calibration is?

I had a great meeting with Lily Zhao (Flatiron) and Megan Bedell (Flatiron) to discuss whether we could write a paper on the term in the error budget in exoplanet radial-velocity projects that comes from wavelength calibration. We have an approach for understanding the impact on radial-velocity measurements from wavelength issues—both biases in the wavelength solution and variances—as a function of the wavelength scale over which those issues are coherent. That's good! But such analyses are of limited use if it is impossible for a project to determine, empirically, how well it is doing in getting those wavelength solutions correct. That is, how do you measure the bias and variance of your wavelength solution, and the covariances across wavelength? That's a hard problem. We discussed approaches that involve calibrating calibration images.