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).
Table of minimum sparking speeds for various post-war Bosch and B.T.H. magneto models.
| Identifier | ExFiles\Box 4\5\ 05-page134 | |
| Date | 28th January 1921 guessed | |
| Contd. -2- post-war models of Bosch magnetos and the B.T.H. type "PM" magneto MINIMUM SPARKING SPEEDS. Full Advance. Full Retard. Angle of Adjustment. Bosch "ZU4" 76 RPM 155 RPM 35Q° Bosch "ZR6" 80 R.P.M. 130 RPM 35Q° Bosch "Z4" 64 RPM 64 RPM 35Q° B.T.H. "PM4" 52 RPM 52 RPM 45Q° | ||