Excel 2013 includes a number of tools to help you troubleshoot the formulas in your worksheet. If things aren’t working out properly or you’re questioning the accuracy of a formula (or Excel displays an error indicator, alerting you to a problem), you can use these tools to find the problem and correct it.
Click the Formulas tab.
In the Formula Auditing group, click the Error Checking tool.
The Error Checking dialog box opens.
Use the controls in the Error Checking dialog box to change the formula or ignore the error.
Click Previous or Next to view the preceding or ensuing error that Excel has found in the worksheet.
Click the Close box to close the Error Checking dialog box and return ...