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).
Sketch illustrating the changing shape of marks or vibrations at different rotational speeds.
| Identifier | ExFiles\Box 154a\2\ scan0226 | |
| Date | 12th December 1939 guessed | |
| 400 ~/min approx 1200 ~/min approx. | ||