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 comparing a standard component with a 4-degree prototype version.
| Identifier | ExFiles\Box 82\3\ scan0287 | |
| Date | 15th May 1935 guessed | |
| Left Diagram: Std GB1222/s 175 275 Right Diagram: 4° proto GDB71/2 125 227 | ||