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).
Instructions for instrument makers on the adjustment and calibration of a speed indicating instrument.
| Identifier | ExFiles\Box 59\2\ Scan136 | |
| Date | 1st April 1931 | |
| EFC2/ADL.4.31. contd. -2- (3) The makers of the instrument must be instructed to adjust the speed indicating portion of the instrument until, when the instrument is at 35°C, and is driven at exactly 607.5 (i.e. 45/60 x 810) R.P.M. of its driving spindle, the speed indicated is exactly 45 miles per hour. N.B. It will be understood that owing to the disproportionality of the scale the internal correctness of the instrument only holds at the speed of 45 miles per hour and that therefore if a check is to be made at any other speed a suitable correction in accordance with our page 10 table must be made, for instance, the drive speed at which it should read 75 miles per hour should be 71.63 / 43.785 x 607.5 = 992 R.P.M.. In putting this specification before the makers it may be implied to them that our drive speed is 810 revolutions per mile in accordance with the 810 for which the instrument is ordered. EFC. | ||