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).
Blueprint graph of performance curves, with the vertical axis representing Mean Effective Pressure (M.E.P.) in LBS per square inch.
| Identifier | Morton\M4.2\ img025 | |
| Date | 1st January 1923 guessed | |
| M.E.P. (LBS. PER SQ. INCH) 90 80 70 60 50 | ||