For the vast majority of the fluorescence and mass spectroscopy CRC data collected for the COVID Moonshot, 4PL+C yields a smaller ASE than 4PL. We fit 1589 of 1668 fluorescence curves and 205 of 238 mass spectrometry curves with a high coefficient of determination, R 2 > 50%, using both procedures. In over 95% of curves of both types, the ASE of R t and R b was lower using 4PL+C than 4PL (Figs. ?? and ??). The 4PL+C procedure provides a lower ASE than 4PL in over 75% of pIC 50 and H estimates. The reduction in ASE suggests that the 4PL+C determines parameters more accurately than 4PL. Log 10 ASE -Proposed Procedure Figure : Comparison of ASE estimates for 4PL+C and 4PL analysis of fluorescence CRC from the COVID Moonshot. For each parameter, the fraction of data above the diagonal is R b (99.69%), R t (98.16%), pIC 50 (89.51%), and H (98.49%).