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 gaps for a push button switch, drawing D.70790.
| Identifier | ExFiles\Box 64\4\ scan0105 | |
| Date | 13th November 1928 | |
| V-76553 13.11.28. PUSH BUTTON SWITCH TO LEE.1904 (D.70790) TABLE OF GAPS. Position. Carbon gap. Copper gap. Button depression. Off .063+12 -13 .090+15 -15 .026" Carbons O .040+5 -5 .055+6 -6 in contact. Coppers O O .078+9 -9 in contact. Obsolete EFC. | ||