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 a Watford speedometer, showing performance at various temperatures.
| Identifier | ExFiles\Box 59\2\ Scan138 | |
| Date | 9th June 1931 | |
| X6051 SPEEDOMETER TEST RECORD. Date :- 9-6-31 Speedometer :- Watford Remarks :- Dial reads up to 100 m.p.h. Drive revolutions per counter mile (found by actual trial) 789 Revolutions per mile specified by makers. 785 Correct miles per hour reading when driving at 600 r.p.m. :- 45.7 Temperature (°C.) M.P.H. indicated at 600 r.p.m. exactly. at 1200 rpm 17 46.5 93.5 20 46.5 24 46.5 26 46.4 28 46.3 30 46.2 32 46.0 34 45.8 Percent fall of reading between 20°C. and 30°C. ..1:5.. | ||