This is an interactive demonstration of Spline fit.

Left click mouse in the plot area to place points.
A minimum of four points are required.

Right click mouse to see the Spline fit.
The value of the integral under the curve is also computed.

Repeat choosing points by left clicking mouse, then
right click to see the Spline fit.

No two points can have the same X value.
Points do not have to be entered in order, they are sorted.

Try radical selections of points to understand the behavior
of the Spline fit.

The window may be enlarged yet the plot area will not be made
smaller than the initial area.

See Algorithm to understand the method.
See Code to read the Java code.
See Options for possible choices.