While you have Excel open, it is constantly checking in the background for potential errors in your worksheets. If an error is located (or, at the least, what Excel thinks is an error), then the cell is "flagged" with a small green triangle in the upper-left corner of the cell.
If you don't want Excel to check for errors, you can turn the feature off by following these steps:
1. Click the File tab at the top-left corner of the window.
2. Display the Excel Options dialog box. (In Excel 2007 click the Office button and then click Excel Options. In Excel 2010 and Excel 2013 display the File tab of the ribbon and then click Options.)
3. Click Formulas at the left side of the dialog box. (See Figure 1.)
Figure 1. The Formulas area of the Excel Options dialog box.
4. Click the box to the left of Enable background error checking to remove the check mark. You can then click the OK button at the bottom of the window to apply your changes.
5. Result..
