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 for a push button switch, detailing gap measurements and button depression at various positions.
| Identifier | ExFiles\Box 70\4\ scan0142 | |
| Date | 13th February 1925 | |
| X8781/ps 13.2.25. X.8781ps. PUSH BUTTON SWITCH. X.8641. (handwritten above: 8651) Position. Carbon gap. Copper gap. Button depression. Off. .040 ±15 .060±20 0 Carbons just in contact. 0 .033 ±10 .020±7 Coppers just in contact. 0 0 .045 ±15 (total) EFC. Issued 13-2-25 | ||