# Looking Up a Single Table Value

Before talking about how the two particular lookup functions that return a single value from a table work, it's important to note that lookup tables are standard data tables in every way except that the following guidelines must be observed:

- The values you want looked up in the table (that is, matched against values entered elsewhere in the worksheet) must be in the first column (in a vertical lookup) or row (in a horizontal lookup) of the data table.
- The values in this first column or row must be sorted in ascending order, by rows from top to bottom in a vertical lookup and by columns from left to right in a horizontal lookup.
- The values in the first column or row must be unique (no duplicate entries allowed here).

Assuming that you set up your lookup table following these three guidelines, you'll have absolutely no trouble getting your lookup formulas to take the correct information out of the table and return it to the appropriate place in your spreadsheet each and every time.