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 record for an A.T. Speedometer.
| Identifier | ExFiles\Box 59\2\ Scan102 | |
| Date | 3rd February 1931 | |
| X6051b A.T. SPEEDOMETER TEST RECORD. Date :- 3.2.31. Speedometer :- D.231 740 11/50 Remarks :- After 10,000 miles on 18-GIV change of reading test. Drive revolutions per counter mile (found by actual trial). 742.5 Correct miles per hour reading when driven at 600 r.p.m. 48.5 Temperature (°C) | M.P.H. indicated at 600 r.p.m. exactly. 16.5 | 46.8 20.0 | 46.5 22.0 | 46.1 24.0 | 45.9 26.0 | 45.7 28.0 | 45.6 30.0 | 45.4 32.0 | 45.2 Percent fall of reading between 20°C. and 30°C... 2.4 14.3.31. | ||