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 various magnetos detailing their types, numbers, and performance speeds.
| Identifier | WestWitteringFiles\F\March1921\ Scan61 | |
| Date | 19th February 1921 | |
| -2- Contd. Magneto. | Type and number. | X. No. | Lowest speeds. | Remarks. | | | Adv. | Cent. | Retd. | ---|---|---|---|---|---|--- R, Bosch. | Z.R.6 | 427 | 260 | 170 | 246. | Advanced position same as maker's. Retarded position 2.5° earlier than maker's. | 2571556. | | | | | U.S.A. Bosch. | Z.R.6 | 3916 | 120 | 162 | 240. | Advanced position same as maker's. Retarded position 3.5° earlier than maker's. | 2998784 | | | | | Dixie. | Aero 648. | 3724 | 180 | 180 | 185. | Sparking speed unaltered by advancing or retarding, hence figures as first obtained on maker's range are representative | 718237. | | | | | Conner. | C.M.1 | 4210. | 350 | 260 | 170. | Retarded position same as maker's, this position giving minimum regular sparking speed. Further retard again increased speed rapidly. Advanced position 14.5° later than maker's | | | | (Weighted averages of two sets of figures). | | B.T.H. | F.M.6 | 3515. | 244 | 192 | 220 | Advanced position 10° earlier than maker's. Further advance limited by fouling of timing lever, but apparently would further reduce the minimum sparking speed in retarded position. Retarded posn 21.5° earlier than maker's. | R.311941 | | | (Weighted averaged of two sets of figures). | | Footer (upside down): R R.{Sir Henry Royce} 235A (60) (T.) I.S.H. 986. 19-2-21 (B) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 3008 | ||