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 and calibration report for a 20 HP Speedometer, detailing issues with readings when hot and cold.
| Identifier | ExFiles\Box 59\2\ Scan001 | |
| Date | 4th January 1930 | |
| X4308. Hs{Lord Ernest Hives - Chair}/AJL. from EFC. EFC/AD4.1.30. X.4308. 20 HP. SPEEDOMETER D.329. 686. 12/50. The revolutions per counter mile were found to be in agreement with the above figure 686. Driven at 600 r.p.m. the instrument was at first found to read 49.8 m.p.h. when cold. To be correct the instrument should read 36000 / 686 = 52.5 m.p.h. when fully warm, and making the percent allowance of 2.85 observed on another recent 20 HP. instrument as the difference between hot and cold condition the correct reading cold should be 54.0. It was found however that the limit of adjustment allowed a reading of only 53.0 without remagnetising, so in view of your requiring the instrument in a hurry we left it in that condition. by R's instruction In regard to these instruments generally in the Experimental, these are the concern of this department, and alterations made to them are only in order if done by ourselves, for which reasonable time must be allowed, and information given of any difference from standard in regard to road wheel revolutions per mile and speedometer gearing. We have been instructed to prove or disprove the case for loss of magnetism in these instruments on cars, but so far we have not had an opportunity of satisfactorily completing a test of this nature. EFC. | ||