For Mouse IL-6 ELISA Kit PicoKine EK0411, if your sample data points are within the middle of the curve, i.e. in the near linear region of the curve, then you can use the best fitting curve out of hyperbola, 4PL and 5PL. However, if your sample data points are near the ends of the standard curve, where it becomes not linear, it is recommended that you use 4PL for fitting, as it best fits the nature of the assay. It is also recommended that you adjust your assay so that the sample data points fall into the middle linear range of the curve. For further troubleshooting you may send us your generated data.