Tables are the simplest and most direct form for presenting economic data. When these data are displayed electronically in the format of an accounting income statement or balance sheet, the tables are referred to as spreadsheets. When the underlying relation between economic data is simple, tables and spreadsheets may be sufficient for analytical purposes. In such instances, a simple graph or visual representation of the data can provide valuable insight. Complex economic relations require more sophisticated methods of expression. An equation is an expression of the functional relationship or connection among economic variables. When the underlying relation among economic variables is uncomplicated, equations offer a compact means for data description; when underlying relations are complex, equations are helpful because they permit the powerful tools of mathematical and statistical analysis to be used.