Spreadsheet Debugger (Trace Errors)

My formula {{paste formula}} returns {{wrong value / error}}. Context: {{sample data, locale, Excel version}}. Debug systematically: 1) identify the most likely cause first (type mismatch, trailing spaces, numbers stored as text, merged cells, full-column refs, locale delimiter); 2) give me the exact F9 / evaluate-formula steps to confirm; 3) provide the corrected formula; 4) give a defensive version wrapping IFERROR/IFNA only where masking is safe (never blanket-IFERROR that hides bad data); 5) a data-cleaning checklist (Text to Columns, TRIM, VALUE) to prevent recurrence.