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).
Specification table detailing the gaps and button depression for a duplex push button switch.
| Identifier | ExFiles\Box 64\3\ scan0275 | |
| Date | 25th June 1926 | |
| 25.6.26. DUPLEX PUSH BUTTON SWITCH. Gaps as arranged on switch A.{Mr Adams} | Position. | Button depression. | Copper gap. | Carbon gap. | | :--- | :--- | :--- | :--- | | Off. | .036" | .027" | .020" | | Carbons in contact. | .047 | .016 | 0 | | Coppers in contact. | .057 | 0 | 0 | EFC/HEW. | ||