A complex analysis generally proceeds within Ferret as a complex hierarchy of expressions: variables defined in terms of other variables defined in terms of other variables, etc., often containing many levels of transformation. When an error message such as "can only contour or vector a 2D region" occurs it may appear difficult to locate the reason for this message.

A simple strategy to locate the source of such problems is to use the command STAT which shows the size and shape of variables and expressions (simply edit the offending command line, replacing the PLOT, CONTOUR, VECTOR, etc. command with STAT and eliminating qualifiers if necessary) and use SHOW VARIABLE to see the variable definitions. By repeatedly using STAT to examine the component variables of definitions one can quickly locate the source of the problem.