From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Graph plotting engine revolutions per minute against vehicle speed in miles per hour.
| Identifier | Morton\M7\ img063 | |
| Date | 5th May 1921 | |
| SION. REVS: PER MIN. 2000 2250 MILES PER HOUR. 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 ROLLS-ROYCE LIMITED -5 MAY 1921 | ||