Detect errors in formulas - Microsoft Support

You can use error checking to detect errors in formulas. The rules don't guarantee error-free worksheets, but they can help find common mistakes. Errors can include: Cells containing formulas that result in an error, inconsistent calculated column formula in tables, cells containing years represented as 2 digits, numbers formatted as text or preceded by an apostrophe, formulas inconsistent with other formulas in the region, formulas which omit cells in a region, unlocked cells containing formulas, formulas referring to empty cells, and data entered in a table is invalid.

How to edit, evaluate and debug formulas in Excel

Detect errors in formulas - Microsoft Support

Formula compatibility issues in Excel - Microsoft Support

Excel Formula Error

Remove or allow a circular reference - Microsoft Support

NUM error in Excel - fixing number error in formulas

Detect errors in formulas - Microsoft Support

Detect errors in formulas - Microsoft Support

Use Excel with earlier versions of Excel - Microsoft Support

Troubleshooting formulas

How to correct a #VALUE! error in the IF function - Microsoft Support

VALUE error in Excel: causes and fixes

UNIQUE function - Microsoft Support