PURPOSE Formula errors can cause incorrect totals, reports, and decisions. COMMON ERRORS Look for divide-by-zero errors, missing references, invalid names, incorrect ranges, hidden rows, and formulas copied incorrectly. CHECK METHODS Review formulas, trace dependencies if available, test with known values, and compare totals to source data. WATCH FOR SILENT ERRORS A formula can be technically valid but logically wrong. Those are the sneaky little spreadsheet goblins. BEST PRACTICE Use clear assumptions and separate input cells from calculation cells.