Histograms of the TOA uncertainties, with TOAs extracted from uncalibrated NUPPI data (“Uncal.”), data calibrated using the SINGLEAXIS method (“Cal.”) and data calibrated with the improved calibration method described in Sect. 2.2 (“Cal. + corr.”). Three of the TOA datasets were derived from the NUPPI data using the FDM algorithm; the other three were extracted using the MTM technique.