I need to prepare function plots in a form German pupils are used to, i.e. with axes of the coordinate system in the middle of the plot instead of at the borders.
For the Gnuplot section I created a solution for this problem with Gnuplot. This here is a newer approach, using not only Gnuplot, but LaTEX, too.
Graph4school-tikz is my template for such a plot. The output is presented as PNG.