SPLOT Algorithm
Model space dataset values are generated by an approximate method
(unavoidably), explained in SPLOT_TRANSFM. Note that the
transformation is only valid if the model is a good fit.
Formatting of plotted output is expressed in terms of 'plot zones'
'plots' and 'graphs'. A 'plot' is a set of axes with one or more
'graphs' plotted on it (i.e. overlaying allows several graphs per plot).
A 'plot zone' is just the collection of plots for a single input
dataset. The total graphical output from the program consists of one
p.z. for each dataset.
Note that the base axes in each plot are set by the observed data. This
may mean that some of an overlaid fit will disappear off the graph.
Graph legends and axis labels etc are propagated from the input datasets
into the plots produced.