Letter from AC-Sphinx Sparking Plug Co. regarding calibration compromises on an instrument.
| Identifier | ExFiles\Box 165\2\ img102 | |
| Date | 10th July 1937 guessed | |
| THE AC-SPHINX SPARKING PLUG Co. LTD. CONTINUATION SHEET No. 2. You will note that we have had to compromise in such a way that at 60 M.P.H. it is reading approximately .2 of a mile higher than your specification, and at 90 approximately .6 lower than your specification. This is, of course, because you call for 5% fast at 90, while only 3% at 60. Checking the reading by the actual number of revolutions required to produce certain miles per hour, your limits at 60 would be 983 to 1002, while we found on our instrument that 995 R.P.M. gave 60 M.P.H. which at this actual point would be within your limits, while at 90 M.P.H. your limits would give 1446 to 1475 R.P.M., while on our instrument it required 1482 R.P.M. to produce 90 M.P.H.. Unfortunately we have been unable to exactly check the reading at 20 M.P.H. as shown on your specification as the required spindle speed unfortunately is just off the scale on our master revolution counter, but appears to be within your limits of 3 to 7% slow. On any future instruments we should of course distort the scale to give the exact reading required, and could then quite easily work within the tolerances named. In the meantime however, as you are urgently requiring the instrument we are despatching it to you without further delay. Yours faithfully, THE AC-SPHINX SPARKING PLUG CO. LTD. D. {John DeLooze - Company Secretary} BENNION BROWNE Chief Engineer P.S. We should be interested to know what results you found on the revolution indicator which was reported to be reading slow, and which you retained for further checks. | ||
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).