This is NOT an error … only something that you might consider.
If you would like to indicate that the value of a cell is an approximate number ( like, for example, you previously put a "+ sign" inside of the cell ), you could change the background color of the cell … some people might call that "highlighting".
Of course, if you do that, you would also need to provide a "Legend" at the bottom of the Spreadsheet, so that people would know that a Yellow Cell ( for example ) is only an approximate value.