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).
Comparative table of relative distributor dimensions for Watford and Lucas models.
| Identifier | ExFiles\Box 65\3\ scan0036 | |
| Date | 13th June 1927 guessed | |
| -4- Contd. Relative distributor dimensions. Watford. | Lucas (jump spark) | Lucas (Wipe contact) | Suggested relative dimensions. Pitch (P) 1.000 | 1.000 | 1.000 | 1.000 Make ratio (M) .690 | .575 | .575 | .56 Range (R) .280 | .333 | .33 | .34 Forward overlap at full advance (F a) .126 | .004 | .165 | .10 Forward overlap at full retard (F r) .406 | .337 | .495 | .44 Backward overlap at full advance (B a). .286 | .182 | .19 | .20 Ditto at full retard (B r) .006 | -.151 | -.14 | -.14 Width of brushes (B) .143 | .427 Length of segment (S) .580 | .183 Brush + segment. .72 | .61 | .78 | .74 B + S + M.{Mr Moon / Mr Moore} 1.41 | 1.185 | 1.355 | 1.30 Insulation distance (I) .404 | .393 | .385 | .36 Distributor dia. (D) 1.910 | 1.910 | 1.910 | 1.910 Contd. | ||