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 | ||
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).