step,rule,n_before,n_after,n_removed,rationale
1,read data/firms.csv,445,445,0,All data rows read (header excluded).
2,drop exact duplicate rows (keep first occurrence),445,400,45,"45 rows were exact copies of another row (same firm_id and all fields), an assembly error; one row per firm kept."
3,convert revenue to millions USD (USD_thousands / 1000),400,400,0,Recoding only: 60 firms reported revenue in USD_thousands; divided by 1000. No rows removed.
4,exclude firms with unknown (empty) revenue,400,394,6,Revenue unknown; cannot contribute to revenue aggregates. Firm IDs: F0048;F0121;F0129;F0269;F0348;F0399