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).
Page of diagrams illustrating various spark and arc characteristics.
| Identifier | ExFiles\Box 63\4\ scan0010 | |
| Date | 26th May 1918 guessed | |
| (10) (37) ZA2/200/2/A/A Sparks. Arc. (38) ZA2/200/2/A/B Sparks and arc. ZA2/200/2/R/A Slightly less arc on retard. (40) ZA2/200/2/R/B Single spark only No arc. (41) ZA2/200/5/A/A Spark regular some arc. (42) ZA2/200/5/A/B Single spark. Trace of arc. | ||