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).
Comparison table of test results for various magnetos, including resistance and output readings.
| Identifier | WestWitteringFiles\F\March1921\ Scan64 | |
| Date | 15th March 1921 guessed | |
| -3- A.{Mr Adams} Contd. (17) Magneto. Contact breaker flinging speed (R.P.M.) (18) Primary resistance (ohms). (19) Secondary Resistance (ohms). (20) Secondary m.a. on C8 Volts 50~ Hor. Vert. (24) Remarks. Watford | .54 at 19°C. | 3319 at 19°C. | - | - | " | .535 at 18°C. | 3057 at 18°C. | 15.5 | 9.4 | " | .51 at 14°C. | 2800 at 15°C. | 20.3 | 9.6 | " | .49 at 16°C. | 2840 at 17°C. | 20.1 | 11.2 | Low speed sparking characteristics taken before endurance test on which test magneto broke down on H.T. brush. R.{Sir Henry Royce} Bosch. | .73 at 15°C. | 2849 at 16°C. | 9.4 | 5.3 | U.S.A. Bosch. | .935 at 20°C. | 3106 at 21°C. | 8.4 | 6.7 | U.S.A. Bosch. | -- | -- | -- | -- | Dixie. | .68 at 16°C. | 3458 at 16°C. | 12.8 | 8.4 | Conner. | .51 at 18°C. | 2400 at 19°C. | 13.6 | 8.1 | B.T.H. | .76 at 14°C. | 2690 at 16°C. | 22.4 | 16.3 | Gap had to be increased to obtain slow speed figures owing to distortion produced on endurance test. | ||