Although curve fitting with the 4PL+C procedure is slower than with 4PL, both are still quite fast. Performing fits for all 1668 fluorescence curves took 6 minutes and 2 seconds for 4PL+C but only 18 seconds for 4PL. For all 238 mass spectrometry curves, the fitting took 36 seconds for 4PL+C versus 8 seconds for 4PL. As described in the methods section, the 4PL+C procedure alternates between optimizing the Hill equation parameters θ and the estimated variances. In contrast, the 4PL procedure only requires optimizing the Hill equation parameters. Nonetheless, 4PL+C is quite fast and the additional computing cost required for the curve fitting should not be a barrier to using the procedure.