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).
Contact breaker timing specifications for Watford IS.12 Aero Magnetos with latest modifications.
| Identifier | ExFiles\Box 43\4\ Scan139 | |
| Date | 14th August 1928 | |
| X 4021 14.8.28. CONTACT BREAKER TIMING OF WATFORD IS.12 AERO MAGNETOS (LATEST MODIFICATIONS 30° RANGE) No. 98033. | Advance | Retard. | |---|---| | Make | 2° | 34° | | Break | 52° | 81° | Make ratio .539. Range 30°. No. 98034. | Advance. | Retard. | |---|---| | Make. | 6° | 36° | | Break | 50° | 80° | Make ratio .489 Range 30° EFC. | ||