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 checking the revolutions per mile of a speedometer.
| Identifier | ExFiles\Box 59\2\ Scan032 | |
| Date | 27th May 1930 | |
| X4308 CHECK OF REVOLUTIONS PER MILE OF SPEEDOMETER. Speedometer :- A.T. No E.187. 785 11/41 40/50 HP from stock Date :- 27-5-30 Mile reading | Counter reading. Observed at finish. | 00301 | 95791 Observed at start. | 00000 | 36674 Difference | 301 | 59117 Counter revs. per mile | 196.4 Instrument revs. per mile. | 785.6 28.10.29. | ||