gnuplot is an axis drawing program, that takes data in ASCII format, and produces fancy graphs. You will need X11 running and a text editor.
I installed this as a Slackware package. For many people it is a standard component.
According to it's own README, the GNU in gnuplot has nothing to do with GNU. Strange, but fair enough.
There are a several demo programs, and datafiles here. Might as well try a few.
Up pops a flattened globe, then a transparent one, then a cylinder.
This is the program that sequences the demo, and draws the graphs.
This is the datafile with the approximate coastal outlines, in 3-d coordinates (latitude, longtitude). Not bad for 16k. Does it fill ??
This is a list of points, marking city and university sites. I wonder what the MX records say ...
This file shows how you could keep comments in datafiles, whilst still sorting and auto-editing the data files.
This cycles through some graphs, ranging from the sinusoidal, to the experimental. Goes through all variations of a type of graph.
This is the online help topic documentation (except for man gnuplot). It explains how to set titles on graphs, what kind of graphs are available, how to call math exprs. how to read files of data-points, and how to generate maths functions.
You can access it using less, or an editor that allows you to search for keywords. It can be run in another VC, whilst you browse the gnoplot command lines, and data files.
This file is manually included in many demos using load "defaults.ini"
After the man and .gih file, the program has a help command. Normally you would read gnuplot commands from a file or pipe. With interactive mode, you just type gnuplot and it gives you a command line prompt, where you can type help, help topic, or any other command.
Whilst I like Slackware, I also like the original packages. If you look on disk3, or prep.ai.mit.edu, you will find /cdrom/gnu/gnuplot-3.5.tar.gz, with loads of files and docs in there.