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).
Specifications and ratios for a duplex push button switch.
| Identifier | ExFiles\Box 64\3\ scan0273 | |
| Date | 24th June 1926 | |
| X. 7650 24.6.26. DUPLEX PUSH BUTTON SWITCH. Fulcrum to button .825" Fulcrum to copper contact. 1.175" Fulcrum to carbon contact. 1.500" Ratio copper contact arm / button arm = 1.425 θ Ratio carbon contact arm / button arm = 1.820 ø Ratio carbon contact arm / copper contact arm = 1.275 ψ EFC/H.E.W. | ||