Excel is a flexible and powerful spreadsheet application. The people I meet in Microsoft Excel training are often in awe of how many different ways they can use spreadsheets to track data.
Excel incorporates many advanced features to ensure users are entering data accurately and consistently. Did you know that Excel incorporates error checking?
The entire time you’re entering text, numbers, formulas, and functions, Excel is scanning your spreadsheet for errors. When Excel encounters an error, it displays a green triangle in the upper-left corner of any cells containing errors.
The screenshot below indicates an error because column D contains numbers stored as text – a common error when you import data from other sources.

Depending on the purpose of your spreadsheet, you may not need to correct the error. Sometimes ignoring the error (and hiding the green triangles) is all you really want to do.
Configuring Error Checking Options in Microsoft Excel
If you want to see the specific errors that Excel checks for, they’re all listed in the Excel Options dialog box. Just select the File tab, click Options, then go to the Formulas tab.
In the bottom part of the dialog box, there are two sections: Error Checking and Error Checking Rules.

Error Checking
The Error Checking section allows you to turn background error check on or off. It also allows you to set the color used for indicating errors.
Error Checking Rules
The Error checking rules section lets you customize the types of errors Excel checks for. You can enable or disable the various checkboxes in this section to indicate which errors Excel checks for.
Ignore Errors with the Shortcut Menu
If you want to ignore errors in specific cells, drag to select the cells with a green triangle, click the Trace Error button, and select Ignore Error from the shortcut menu.
Using this option to ignore errors is specific to the cells selected. After ignore error is selected, the green triangles disappear from the specified cells.

Disable Error Checking to Ignore Errors
In the Excel Options dialog box, you can enable or disable error checking by selecting or deselecting the checkbox beside Enable background error checking.
To ignore errors globally, select the File tab on Excel’s ribbon, click Options, then go to the Formulas tab. Clear the checkbox beside Enable background error checking then click OK.

Resume Error Checking: Reset Ignored Errors
If, at any time, you want to resume error checking in your spreadsheet simply display the Excel Options dialog box, go to the Formulas tab, click the Reset Ignored Errors button, and click OK.