In a chart that displays lines (Line type or X-Y type), you can choose to show curves instead of straight lines. Some options control the properties of those curves.
In the Chart Type dialogue box of a Line chart or X-Y chart that displays lines, choose Stepped in the Lines type drop-down, then click the Properties button.
Press Shift+F1 and point to a control to learn more about that control.
These are mathematical models that influence the display of the curves. The curves are created by joining together segments of polynomials.
Optionally set the resolution. A higher value leads to a smoother line.
For B-spline lines optionally set the degree of the polynomials.