Automatic Waveform Measurement > Fitting a Curve to a Graph
Linear, single-, double-exponential functions or Boltzmann functions can be fitted to an X/Y graph using non-linear least squares curve fitting.
To fit a curve to the displayed X/Y graph:
1) Select the type of curve(linear, exponential, two exponential or Boltzmann) to be fitted from the fitting equations list. 
2) Define the region within the graph to which the curve is to be fitted using the pair of (f-f) vertical analysis region cursors. The selected region is indicated by the horizontal bar at the bottom of the display.
Note. For exponential functions, also define the initial starting point of the fitted curve, using the x0 cursor.
3) Click the Fit Curves button to start the curve fitting process. The initial parameter guesses are displayed in the Set Fitting Parameters dialog box.
If you want to keep a parameter fixed (i.e. not changed by curve fitting process) tick its Fixed box. You can also change the initial parameter guesses, if they appear to be unrealistic. Click the OK button to fit the curve.
The best fitting curve is superimposed on the X/Y graph (in red) and the best fit equation parameters are displayed in the Curve Fitting table, along with the parameter standard error, the residual standard deviation (between the fitted and data points), statistical degrees of freedom in the fit, and the number of iterations it took to find the best fit.
