In the course of your commentary on page 130 of the February issue you express curiosity as to how I manage to keep meticulous notes of times and distances when driving solo and fast. There is no mystery about this and recording the necessary data presents no problems. For each journey I buy a new notebook—couldn’t face the possibility of losing records of previous trips—and keep it on or beside the seat, together with a pen or pencil or two.
When starting the journey the petrol tank is brimful and the trip recorder is zeroed. I take on fuel at the longest possible intervals and always refill the tank to the brim, recording the exact quantity and the trip reading. This is the only satisfactory method of determining petrol consumption—dividing the mileage covered by the petrol put in to fill the tank, Each time I make a stop I record the time of stopping and restarting. All the data so far mentioned are recorded while the car is stationary. Times and distances I scribble down whilst driving without taking my eyes off the road—peripheral vision tells me that my pen is actually on the paper. Sometimes these notes are almost illegible, but I go over them at each stop and correct or erase doubtful entries.
When I have finished my journey I go through all the entries and make summaries and calculations. It does not require a tremendous number of entries in the notebook to produce a detailed account and analysis of a journey. It is necessary to have an appreciation beforehand of what facts and figures will be needed and as I am an accountant by training I suppose I must have an aptitude for this sort of thing. I remember, for example, that I restarted after lunch at, say, 1237 and make a mental note to record the mileage at 1337—or at 1307 if it happens to be a fast stretch—and at 1437, and so on. I also have in my mind the cumulative time of stoppages and the time I started the journey, so it is easy to remember when to note mileages at each hour of elapsed driving time. In order to check the accuracy of my trip recorder I make a note, as I enter a stretch of autoroute how many kilometres it is to the next big town on the signboards, e.g. “Lyon 312”, and note the trip reading, say 141.2 (miles). Before reaching Lyon I repeat the exercise— “Lyon 12” on the road signs and (say) trip reading 320.8 miles, thus 300 kilometres on the road have been recorded on the car as 179.6 miles instead of the correct figure of 186.4 miles. Simple arithmetic then determines the extent to which the instrument is over- or under-recording. (Not all the road signs are reliable, so it is advisable to take intermediate checks and not to leave it until one is almost at the end of the autoroute before making the observations, as the signs have a habit of drying-up some distance before then.)
It is also possible to check the accuracy of the speedometer with the aid of a split-second chronograph by driving with the needle kept steady on 60, 70, 80, etc. and observing the time taken to cover 1 km., 2 km. or more according to road and traffic conditions. At high speeds an error of one-fifth of a second is unacceptable, so that it is not possible to make accurate observations when driving solo. Quite accurate assessments can be made, however, when a passenger does the timing.
I enclose my notebook recording a journey to the South of France just before Christmas in a new Rolls-Royce Silver Shadow which I think will bear out what I have written . . . Have I answered your question?
It has occurred to me that it would be easier to use a tape recorder, but this would preclude reference to recorded data during the trip and I hesitate to imagine my feelings if it failed and I finished up with nothing!
Cobham. Stanley Sedgwick.