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).
Test report on an A.T. Speedometer C.83 from chassis 20-EX, detailing reading discrepancies and temperature effects.
| Identifier | ExFiles\Box 59\2\ Scan085 | |
| Date | 31th October 1930 | |
| X4308. Hs{Lord Ernest Hives - Chair}/AJL. from EFC. EFC7/AD31.10.30. X.4308. A.T. SPEEDOMETER C.83. 800. 14/52. The above instrument has been removed from chassis 20-EX for test. The counter revolutions per mile found by actual trial are 792 (though the instrument is marked 800). We have carefully confirmed this discrepancy by working this figure out from the numbers of teeth on the internal gears. We shall probably write to the makers concerning this discrepancy The correct mile per hour reading corresponding to the figure 792 is 45.4. Below we give a table of the miles per hour readings indicated at various temperatures when the instrument is driven at 600 R.P.M. :- Temperature (°C.) M.P.H. indicated. 17.0 46.6 20.0 46.2 22.0 46.0 24.0 45.8 26.0 45.7 28.0 45.5 30.0 45.3 32.0 45.1 You will see from the table that the instrument is correct in itself at about 29°C. and that the temperature error is reasonably small. If, on the car, the instrument is driven on the average at 800 revolutions per mile, the mileage reading will be 1% high and the speed reading will be 1% high at 29°C. with errors at other temperatures as indicated by thr above table. EFC. | ||