Overbars allow you to format special characters, such as "X-bar," which is commonly used to represent the mean or average of a series of numbers. Although, you can use Excel's Equation Editor to create complex equations, the results appear in a floating box, rather than inside an actual cell. Aside from the added complication in using this method, this makes referencing the text more difficult. A more user-friendly approach is to add an overbar to regular text using a unique combination of font types.
Open Microsoft Excel and click the cell where you want the overbar letter to appear.
Click the font drop-down menu on the Home tab and select the "Symbol" font.
Type a grave accent, which is usually located just above the Tab key on your keyboard.
Click the font drop-down menu again and select the font you want to use for the letter.
Type the letter you want formatted with an overbar and press "Enter." Excel automatically converts the two symbols into one overbar letter, such as "X" appearing with a line over it.