Data for this graph are entered by doing fun catwt at the
Linux command line.
This invokes ~funnell/fun/catwt.tcl which requests a cat's
weight and appends it to ~/public_html/catwt.gnuplot_data,
and then invokes gnuplot ~/public_html/catwt.gnuplot to create
~/public_html/catwt_mostRecent.png,
~/public_html/catwt_from201801.png and
~/public_html/catwt.png.