+The @subcmd{SPREADLEVEL} plot displays the interquartile range versus the
+median. It takes an optional parameter @var{t}, which specifies how the data
+should be transformed prior to plotting.
+The given value @var{t} is a power to which the data is raised. For example, if
+@var{t} is given as 2, then the data will be squared.
+Zero, however is a special value. If @var{t} is 0 or
+is omitted, then data will be transformed by taking its natural logarithm instead of
+raising to the power of @var{t}.
+