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).
Investigation into the increased reading of an A.T. Speedometer and its performance at various temperatures.
| Identifier | ExFiles\Box 59\2\ Scan082 | |
| Date | 3rd October 1930 | |
| Hs{Lord Ernest Hives - Chair}/AJL. from EFC. c. Hs.{Lord Ernest Hives - Chair} X4308 EFC2/AM 3.10.30. X.4308. A.T. SPEEDOMETER E.185. 785. 11/41. This instrument is a production instrument which we have taken out from the Stores for fitting to chassis 23-EX to replace instrument A.677 N.800 at present thereon whose reading had increased and the reason of which increase we have desired to further investigate. The counter revolutions per mile were checked and found to be 785.0. When the instrument is driven at 600 R.P.M. the correct miles per hour reading corresponding to this figure should be 45.8. Below we give a table of the actually observed miles per hour reading at 600 R.P.M. exactly at various temperatures, from which it will be seen that the percentage fall of reading between 20°C and 30°C. is 1.5 Temperature (°C.) M.P.H. indicated at 600 r.p.m. exactly. 17.0 47.9 20.0 47.5 22.0 47.3 24.0 47.1 26.0 46.9 28.0 46.8 30.0 46.8 32.0 46.6 It will be seen that the instrument in itself is reading slightly high at all temperatures but by an amount which at 32°C. is not serious. On the car the instrument will probably be driven at above 800 revolutions per mile, in which case | ||