Older versions of gnuplot ran into a problem when dealing, for example, with datafiles whose content is subject to change. When using gnuplot to examine such volatile data interactively, we might want to zoom in or out, or add a title to the plot to prepare it for saving. The problem is that each of these operations either requires an explicit call to
replot or, in the case of mouse operations, calls it implicitly. And when the
replot command is issued, the datafile is read anew, and the new data is plotted. What if we want to manipulate the plot while retaining the data already read in?
The new features in gnuplot version 4.4 for dealing with volatile data were added with these issues in mind.