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Data tables are a built-in tool in Excel that allow you to "stress test" spreadsheet model outputs by automatically recalculating the output value under various assumptions. Data Tables allow you test "what-if" scenarios independently of the case model. For example you might want to test the impact of changing price or cost on profit.
As the name suggests a one variable or one way data tables allow you the change one input and examine the impact on an output. Results can be graphed or have conditional formatting applied for easy interpretation.