Curve fitting routines help depict trends in your data. Select pre-defined fits or define a custom fit to add to the graph. Display fits for Line and Scatter Graphs, Step Plots, Polar Graphs and Histograms. There are 11 pre-defined curve-fitting algorithms in Grapher: 

Linear	Logarithmic	Exponential
Power	Spline Smoothing	Polynomial Regression
Orthogonal Polynomial Regression	Linear through Origin	Running Average
Weighted Average	Gaussian (available only for histograms)

Associate any number of fits with a single curve. Change the line style, color and width for each fit. Applicable statistics are available for each fit. The resulting statistics are copied to the clipboard or displayed in a report window. Export fit curve data to a worksheet to calculate additional statistics. Change the range of data used to create the fit curve and the range of values to display the fit curves individually. 

Add confidence intervals to your fit curves to show the degree of confidence that is in the fit.  Fill between confidence upper and lower bounds to highlight the certainty.