How do i put a overline on top of a letter in microsoft excel?

Hi, and welcome to Fluther.

It’s not at all certain that you can do what you want to with most commercially available fonts, including all of the fonts that ship with Microsoft products in the USA.

But to answer your question more generally: You need a font set that supports the character you want to make. It’s as simple as that. Offhand, I don’t know of any of the common fonts that do offer the “long i” sound mark you seem to want.

The company I work for has a unique way of representing its name, and has developed an internal font to enable us to write the company name “in logo type” whenever that is called for.

I know there is a way with Microsoft Equation Editor, which works within Word and Excel. If I recall correctly it kind of creates a picture of your equation (which in this case would be VICO typed as if they are variables), and the picture is then pasted into the document.

You might also be able to do it with the Unicode character Combining Overline U+0305

http://en.wikipedia.org/wiki/Overline
http://www.fileformat.info/info/unicode/char/305/index.htm

I don’t have Word or Excel on the machine in front of me so I can’t test this. So let us know if it works!