A twoway data table, also called a twovariable data table, is a tool used in Excel to perform a 'whatif' analysis on the effects of changes in any two variables on the output of a formula. This eliminates the need to retype variables in formulareferenced cells numerous times to see the outputs of various possibilities, or to copy and paste a single formula many times in reference to different variable combinations.
Creating a TwoWay Data Table

After deciding which variables and formula to test, list all the values of your first variable vertically, from top to bottom, in any column, and all the values of second variable horizontally, beginning one column above and one row to the right of the first value of your first variable.
Create or copy your desired formula immediately above the first value of the first variable. Your formula may reference any information that you've entered in other cells, depending on the purpose of your data analysis.
Highlight all cells enclosed by your horizontal and vertical variable lists, then click 'Data > Data Tools > WhatIf Analysis > Data Table' to access the data table dialog box.
Enter the input cell for the first variable in the 'column input cell' box, and the input cell for the second variable in the 'row input cell' box. The input cell will be the cell location of the value that you wish to be replaced by each of the respective variables in the whatif analysis.
Click 'OK' in the data table dialog box, and Excel 2007 will fill in all the cells between your two variable lists with the corresponding outputs of the given formula based on the variables listed in the specific output cell's column and row.
Example

As a simple example, to compare the effects of different combinations of three possible unit costs and sales prices on your company's gross margin, you could list the three possible costs vertically, and the three possible sales prices horizontally.
In the example, you would already have an income statement prepared on the same worksheet that lists values for cost, price, unit sales, and gross margin. You would then copy, or retype, the formula from the original gross margin cell directly above the first value for possible costs in your table, since this is the value that you wish to monitor.
In the data table dialog box, the column input cell would be the location of the original 'cost' value in the previously created income statement. The row input cell would be the location of the original 'sales' price value. After clicking 'OK', you would then be able to see the gross margin values for all nine combinations of unit cost and sales price at a glance.
Considerations

According to faculty.fuqua.duke.edu, an XY chart is a great way to visually spot trends and areas of opportunity brought to light in your data table, since this type of chart can use twovariable combinations to chart single points. To create an XY chart, first highlight the group of cells in your table that you wish to chart, then click 'Insert > Charts > Scatter'.
References
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