SECM Cornut-Lefrou Approach Curve Fitter FuNIILab SECM Approach Curve Fitter SECM Cornut-Lefrou Approach Curve Fitter Paste distance-current data, fit a negative-feedback SECM approach curve, and extract tip radius, surface offset, bulk current, residual error, and normalized approach curve parameters. Fit results Tip radius, a- Surface offset, z0- Bulk current, i_inf- RMSE-