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).
Page detailing the mathematical calculations for correcting a speedometer scale.
| Identifier | ExFiles\Box 59\2\ Scan125 | |
| Date | 23th March 1931 guessed | |
| -5- If the amount of the contraction were in accordance with the already mentioned approximate estimate of 3% between dead slow and 90 miles per hour this would mean, so far as the top end of the scale is concerned, that the figure 90 must be placed against the 87 miles per hour division of an unmodified or proportional scale. d_o the unmodified deflection corresponding to 90 miles per hour is then 90 divisions and d the modified deflection corresponding to the same speed is 87 divisions, whence we have the numerical equation :- 87 = 90 - k.90^2 or k = 3/90^2 = 1/2700 = .00036 (approximately) Therefore, finally the rule for the placing of any figure representing the modified miles per hour reading is d = d_o - .00036 d_o^2 From this relation may be calculated, for every value of d_o i.e. the miles per hour reading on the original proportional scale, the number d of divisions on that proportional scale at which the figure d_o should now be placed to produce the scale contracted in accordance with the above developed law. On account of the fact that certain of the figures contained therein will be subsequently required, such a table calculated for every 10 miles per hour increment of speed is given below :- | ||