ArtSGraph allows you to export coefficients of cubic spline which you plotted or wish to plot.
Use Command -> Export coefficients.
Select array label and enter name of the file to export data to. If you check Header checkbox on, the first line of the file will contain column headers. Click Export to produce a tab-separated file.
The lines of the file contain 6 numbers each – the beginning and the end of each spline segment and 4 spline coefficients of a cubic parabola constructed on the segment (starting from the absolute term). For instance, the line
1 1.1 15.1 -4.26 5.41 -0.47
means that segment 1 ≤ x ≤ 1.1 contains cubic parabola with equation
15.1 - 4.26x + 5.41x2 - 0.47x3