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).
The testing and calibration of an A.T. Speedometer.
| Identifier | ExFiles\Box 59\2\ Scan011 | |
| Date | 3rd February 1930 | |
| X 4308 3.2.30. X.4308. A.T. SPEEDOMETER A.677. N.800. 14/52. This instrument has been tested for gear ratio to counter and mile per hour readings at 600 and 1200 R.P.M. exactly, previously to its going on 10,000 mile test car 23-EX The gear ratio to counter is 800.8 revolutions per mile. We have set the mile per hour readings to be 44.8 at 18°C. at 600 R.P.M. and at this setting it is 42.8 m.p.h. at 30°C. The instrument is therefore now correct in itself i.e. reads 45.0 m.p.h. at 600 r.p.m., at 16°C. Driven at 836 revolutions per mile at 600 R.P.M it will indicate speed correctly (viz. 43.0 m.p.h. when at 28°C. and mileages 4.5% high. At 18°C. the speed reading will be 4.1% high and the mileage reading as above. EFC. | ||