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).
The lever lengths and ratios for a main and relay switch unit.
| Identifier | ExFiles\Box 64\4\ scan0115 | |
| Date | 12th December 1928 | |
| X7655B EFC/T8.12.28. MAIN AND RELAY SWITCH UNIT. LEVER LENGTHS AND RATIOS. Relatively. MAIN SWITCH. Fulcrum to side lug (core centre) = 1.500" 100 Fulcrum to core stop = 1.825" 122 Fulcrum to copper contact = [s]2.400[/s] 2.500 [s]160[/s] 167 Fulcrum to carbon contact = 2.900" 193 Ratio copper contact arm / core stop arm = 1.32 Ratio carbon contact arm / core stop arm = 1.59 Ratio carbon contact arm / copper contact arm ≠ 1.21 Ratio core stop arm / side lug arm = 1.22 RELAY SWITCH. Fulcrum to core centre = 1.500 100 Fulcrum to core stop = 1.775 118 Fulcrum to upper contact = 2.100 140 Fulcrum to lower contact = 2.500 167 Fulcrum to carbon contact = 2.875 192 Ratio upper contact arm / core stop arm = 1.18 Ratio lower contact arm / upper contact arm = 1.19 Ratio carbon contact arm / lower contact arm = 1.15 WFW | ||