AbstractHere I discuss progress in both the theory and practice of data analysis for the Hydrogen Epoch of Reionization Array (HERA), focusing on techniques to calibrate the instrumental response and preserve the spectral smoothness that is essential to separating the cosmological 21 cm signal from foregrounds that are five orders of magnitude brighter. I explain how mis-calibration can create ruinous spectral structure and how we take advantage of HERA’s highly-redundant configuration for calibration. This proceeding draws from a talk I gave on October 3, 2017. Slides for it and all my talks are available atjoshdillon.net.