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).
Graph of make-ratio speed curves for a U.S.A. Bosch contact breaker at two different gap settings.
| Identifier | ExFiles\Box 61b\4\ scan0148 | |
| Date | 19th October 1927 | |
| MAKE RATIO .1 .2 .3 .4 .5 SPEED (r.p.m.) 400 800 1200 1600 1800 .010" GAP .020" GAP MAKE-RATIO SPEED CURVES OF U.S.A. BOSCH CONTACT BREAKER. H.E.W. 19-10-27 | ||