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).
Cost comparison for two different types of valve springs.
| Identifier | ExFiles\Box 148\2\ scan0281 | |
| Date | 24th January 1940 | |
| 1260 24.1.40. Cost of valve springs :- EB.175 Chrome Vanadium - Made in Works. 1/4d. EB.3256 Carbon Wire valve springs. Bought Out 5½d.{John DeLooze - Company Secretary} ........ RM{William Robotham - Chief Engineer} | ||