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.
Select Cubic spline or B-spline.
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.