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).
Diagram illustrating the correct settings and dimensions for a spark gap.
| Identifier | ExFiles\Box 167\2\ img086 | |
| Date | 4th December 1937 guessed | |
| SPARK GAP SETTING HIGH TENSION POINT 0·1 - 0·3 MIN. 0·05 - 0·10 MIN. EARTH POINT 54-56° IONISING POINT 54-56° CORRECT | ||