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).
Letter from the A.T. Speedometer Co. comparing the temperature performance of their speedometers against Smith 'Nemag' instruments for Bentley Chassis.
| Identifier | ExFiles\Box 59\2\ Scan226 | |
| Date | 16th August 1933 | |
| The A.T. SPEEDOMETER Co., Ltd. MAGNETIC SPEEDOMETERS & Motor Clocks. REVOLUTION INDICATORS FOR MOTOR CARS, MOTOR BOATS, AND ENGINES, MILEAGE RECORDERS, ETC. DIRECTORS. W. Henderson-Cleland. A.{Mr Adams} Gordon Smith. H.{Arthur M. Hanbury - Head Complaints} R.{Sir Henry Royce} Buckland. CHRONOS WORKS, NORTH CIRCULAR ROAD. LONDON. N.W.2. Telephone: GLADSTONE 1136 (4 Lines). Telegrams: Aytespeedo, Crickle, London. YOUR REF. Hs{Lord Ernest Hives - Chair}/Wst.S/MJ. PLEASE QUOTE OUR REF. HRB/DC ALL COMMUNICATIONS TO BE ADDRESSED TO THE COMPANY. [Handwritten: 86051] [Handwritten: WST] [Handwritten: See me] [Handwritten: HS{Lord Ernest Hives - Chair}] 16th August, 1933. Messrs. Rolls-Royce Ltd., DERBY. Dear Sirs, Re - A.T.Speedometers for Bentley Chassis. We duly received your letter of the 10th instant, giving details of comparisons between the A.T. and the Smith "Nemag" instruments in regard to temperature, and we beg to reply as follows - (1) Variation of reading with temperature. The comparative figures are interesting and as you state, the "Nemag" shows the variation of 3%, and over the same variation the A.T. shows over 5%. We should like to point out, however, that the "Nemag", it seems, was no less than 4% fast at the lower temperature (35°C.), whereas the error on the A.T. instrument was such that the mean accuracy was surely better. For instance, the A.T. was only 1.5% fast at 35°C., which is a fairly average scuttle temperature, but the "Nemag" was 4% out. No doubt during these tests you will arrive at figures which will give you an indication of the average temperature at which the Speedometer will be running, and if you could let us have that figure together with your ideas as to variations on same, we will install tests here which will poise the Magnet in such a way as to give the lowest possible variations. We have always found that the A.T. heavy Magnet has been exceptionally consistent in regard to temperature variations, but it will in any case improve Cont'd......... | ||