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 report on a Watford 100 m.p.h. magnetic type speedometer.
| Identifier | ExFiles\Box 165\4\ img103 | |
| Date | 9th June 1931 | |
| X 6129 To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/HEW. c. Sg.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} c. E.{Mr Elliott - Chief Engineer} De. c. Ey. PN.{Mr Northey} Hs{Lord Ernest Hives - Chair}/HEW2/AML 9.6.31. WATFORD 100 m.p.h. MAGNETIC TYPE SPEEDOMETER. We have tested a sample speedometer submitted by Messrs. North which works on the same principle as the A.T. The instrument has been tested for accuracy and percentage drop of reading with rise in temperature. The m.p.h. reading is dead correct at the highest instrument board temperature attained on our chassis during hot weather and reads 1.5% high at normal atmospheric temperature. At the high speed end of the scale the reading is 2.3% high. This is precisely what is required on the P.2. as it is estimated that centrifugal force on the tyres causes the reading to drop slightly at high speeds. The accuracy is equally as good as the A.T. and the percentage drop with temperature not as much as the average figure obtained on A.T. instruments (see attached curve). The mileage recorded reads correct miles when driven at 789 revs. per mile. As this instrument is quite accurate and represents a big saving over the A.T., we propose to get an instrument made up to suit our standard instrument patch for test on a chassis. Hs{Lord Ernest Hives - Chair}/HEW. | ||