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).
Test results for governed ignition timing, comparing different spark plug positions.
| Identifier | ExFiles\Box 37\1\ scan 225 | |
| Date | 10th March 1921 | |
| X.3949. 10.3.21. Hs.{Lord Ernest Hives - Chair} RE GOVERNED IGNITION. Further tests as below:- | Intermediate Plugs. | Plugs over inlet valves. R.P.M | Retard. | Advance. | Retard. | Advance. 500 | 10° | 20° | 10° | 21.5° 1000 | 16° | 25° | 17° | 29° 1500 | 18° | 31 | 22° | 37° TCMW. | ||