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).
Bench test results for a Phantom II A.T. Speedometer showing speed indications at various temperatures.
| Identifier | ExFiles\Box 59\2\ Scan035 | |
| Date | 4th June 1930 | |
| X4308. Ry. from EFC. c. Hs.{Lord Ernest Hives - Chair} c. Wor.{Arthur Wormald - General Works Manager} EFC2/AD14.6.30. X.4308. A.T. SPEEDOMETER 40/50 HP. The following is the result of bench test on an up-to-date Phantom II speedometer E.187. 785 11/41 taken from stock. The instrument was found to be correct in regard to its 785 spindle revolutions per counter mile, the actual figure found being 785.6. The speed indications of the instrument at 600 R.P.M. exactly were found at various temperatures to be in accordance with the following table, from which it will be seen that the temperature error is now still further reduced to a degree which we did not think the makers were able to produce i.e. very little more than 1% between 20°C. and 35°C. Temperature (°C) | Miles per hour indicated at 600 R.P.M. exactly. ---|--- 20.0 | 45.9 22.0 | 45.8 24.0 | 45.7 26.0 | 45.5 28.0 | 45.5 30.0 | 45.4 32.0 | 45.4 35.0 | 45.4 The instrument was correct in itself at 22°C. so that its speed indication was slightly low in relation to its counter miles/ The exactly correct speed at higher temperatures. | ||