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 performance and recalibration of an A.T. Speedometer at various temperatures.
| Identifier | ExFiles\Box 50\4\ Scan188 | |
| Date | 24th March 1928 | |
| To Hs {Lord Ernest Hives - Chair} /AJL. X4308 EFC {E. Fowler Clarke - Electrical Engineer} 2/T24.3.28. A.T. SPEEDOMETER B.138. N730. 15/52. FOR 12EX. We found that we could improve this instrument and have done so and made it read higher to suit the special figures which you gave us. The reason of the irregularity appears to have been slight intermittent friction in the counter drive and now the instrument is much steadier. Its performance now, as re-set by us, is such that it reads correctly (i.e. 48.9 m.p.h.) to your special figure at 27½°C, and at other temperatures, in accordance with the table below, following a straight line law, from which you will see that the fault (crossed out) of reading between 18 and 30°C is 6%. Other instruments have been 5%, and the minimum we ultimately hope for is 4%. Temp. M.P.H. at 600 R.P.M. 18.0°C. 51.3 22.5°C. 50.1 27.5°C. 48.9 30.0°C. 48.25 B138 EFC. {E. Fowler Clarke - Electrical Engineer} | ||