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).
Tables specifying the operational gaps and button depression for a duplex push-button switch.
| Identifier | ExFiles\Box 64\3\ scan0285 | |
| Date | 15th July 1926 | |
| 15.7.26. DUPLEX PUSH BUTTON SWITCH TABLES. Position | Button depression. | Copper gap. | Carbon gap. --- | --- | --- | --- Off. | A | B | ψ (B - C) Carbons in contact. | A + (B-C)/e | C | 0 Coppers in contact. | A + B/e | 0 | 0 Specified gaps. Position | Button depression. | Copper gap. | Carbon gap. --- | --- | --- | --- Off. | A + .000 | .035+5 -3 | .019+13 -8 Carbons in contact. | A + .010+7 -4 | .020+3 -5 | 0 Coppers in contact. | A + .024+4 -2 | 0 | 0 where A = initial button depression. EFC/HEW. | ||