All predefined Fit Curves are listed in this table. You also can specify custom fit equation. Unlike custom fit equations these curves can be adjusted with mouse on Fit Plot.
Name  Formula  Parameters Meaning  Additional Properties 

Line  a — linear b — constant  
Parabola  a — quadratic b — linear c — constant  Vertex: 

Spline  Natural cubic spline, on each ith piece:  xN — anchor point xcoordinates yN — anchor point ycoordinates  
Gaussian  a — amplitude dx — half width at half maximum (HWHM) x0 — maximum position  Area (integral): Standard deviation: 

GaussianA (areanormalized)  a — area (integral) dx — half width at half maximum (HWHM) x0 — maximum position  Amplitude: Standard deviation: 

Lorentzian  a — amplitude dx — half width at half maximum (HWHM) x0 — maximum position  Area (integral): 

LorentzianA (areanormalized)  a — area (integral) dx — half width at half maximum (HWHM) x0 — maximum position  Amplitude: 

Gauss Derivative  Parameters are the same as for original Gaussian: a — amplitude dx — half width at half maximum (HWHM) x0 — center position  Area of original Gaussian (second integral): Standard deviation: Peaktopeak horizontal: Peaktopeak vertical: 

Lorentz Derivative  Parameters are the same as for original Lorentzian: a — amplitude dx — half width at half maximum (HWHM) x0 — center position  Area of original Lorentzian (second integral): Peaktopeak horizontal: Peaktopeak vertical: 