In torrent and academic sharing circles, "PDF4.1" or "v41" sometimes denotes a re-scanned or OCR-processed version. A "better" PDF41 implies:
Often cited as "Hirschfelder et al." with corrected tables and expanded notation.
Whether you are a graduate student or a seasoned chemical engineer, having a copy of is a rite of passage. While seeking a "better" PDF version for portability is common, the value lies in the rigorous, uncompromising math that defines the field.
A better copy will show the equations correctly. In the “pdf41” version, you may see: