From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 8 Jun 2001 19:16:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 8 Jun 2001 19:16:43 -0400 Received: from alcove.wittsend.com ([130.205.0.20]:28310 "EHLO alcove.wittsend.com") by vger.kernel.org with ESMTP id ; Fri, 8 Jun 2001 19:16:33 -0400 Date: Fri, 8 Jun 2001 19:16:00 -0400 From: "Michael H. Warfield" To: "Albert D. Cahalan" Cc: "Michael H. Warfield" , Chris Boot , mirabilos {Thorsten Glaser} , "L. K." , "linux-kernel@vger.kernel.org" Subject: Re: temperature standard - global config option? Message-ID: <20010608191600.A12143@alcove.wittsend.com> Mail-Followup-To: "Albert D. Cahalan" , "Michael H. Warfield" , Chris Boot , mirabilos {Thorsten Glaser} , "L. K." , "linux-kernel@vger.kernel.org" In-Reply-To: <20010608140553.C20944@alcove.wittsend.com> <200106082116.f58LGd2497562@saturn.cs.uml.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.2i In-Reply-To: <200106082116.f58LGd2497562@saturn.cs.uml.edu>; from acahalan@cs.uml.edu on Fri, Jun 08, 2001 at 05:16:39PM -0400 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 08, 2001 at 05:16:39PM -0400, Albert D. Cahalan wrote: > The bits are free; the API is hard to change. > Sensors might get better, at least on high-end systems. > Rounding gives a constant 0.15 degree error. > Only the truly stupid would assume accuracy from decimal places. > Again, the bits are free; the API is hard to change. Twice a year I'm a judge at science fairs. Once at the local level and once at the state level. I generally judge on the senior level in the physics category. All too often I have a hard time even convincing some of my fellow judges. Each year there is at least one project where some student has used "fancy scientific equipment" to make measurements of impressive precision and beautiful results. Till you look closer and you find that their standard deviation is as large as their averages and their raw test results are all over the map. With 5 or more decimal places of precision, you find that their sample sizes and proceedures don't even support one or two decimal places, if they are lucky. If it were not for the fact that I don't think they are really that good at it, I would give them an award for "if you can't dazzle them with brilliance, baffle them with bullshit". Unfortunately, they honestly don't KNOW the difference between precision and accuracy. We often judge between a half a dozen and a dozen exhibits. This comes up every year and gets written up in comments every year. Of course, you can't be harse in judging these things and most of them really do make a legitimate effort, but it is difficult to tactfully explain to someone why their elaborate and extremely detailed results amount to utter jibberish. (To the smartasses who are about to fire off the obligatory smart remarks: Trust me, I am much more tactful with those students than I am on this list... Maybe I shouldn't be. Read that either way.) What's more apalling is that their teachers did not catch this and I have to point out the fatal flaws to a lot of my co-judges who were impressed with the scientific prowess of these individuals. No... The average person, NO, the vast majority of people, DO assume accuracy from decimal places and honestly do not know the difference between precision and accuracy. I've had comments on this thread in private E-Mail the reinforce this impression. Yes, bits are free, sort of... That's why an extra decimal place is "ok". Keeping precision within an order of magnitude of accuracy is within the realm of reasonable. Running out to two decimal places for this particular application is just silly. If it were for calibrated lab equipment, fine. But not for CPU temperatures. Yes, APIs are difficult to change. But can you honestly say that, even if we magically get off the shelf economical temperature sensors that are two orders of magnitude more accurate (without need of constant tracible recalibration - these things DO drift), that this level of precision would have any real meaning at all? I would expect the CPU temperature to vary by a few hundreths of a degree just by how many people were sweating in the cube next to me. Even the rounding error vis-a-vis the .15 is silly and irrelevant! If the sensor is +- 1 degree, you can't even measure the rounding error, even if you HAVE two decimal places. With that degree of accuracy, you are no better off than 273 with no decimal places. Worrying about rounding error on .15 when the accuracy is in the units is exactly the kind of misinformed false precision that I worry about. You actually though that the .15 was significant enough to worry about round error when, in fact, it will be impossible to measure with the equipment available in the environment of discourse. > One might provide other numbers to specify accuracy and precision. Now... That I can agree with and it would make absolute sense. Especially if we were discussing lab grade or scientific grade measure equipment and measurements. In fact, that would be a requirement for any validity to be attached to measurements of that level of precision. But that's not what we are talking about here, is it? We're not talking about a lab grade instrumentation API here, are we? If we are, then everything changes. Mike -- Michael H. Warfield | (770) 985-6132 | mhw@WittsEnd.com (The Mad Wizard) | (678) 463-0932 | http://www.wittsend.com/mhw/ NIC whois: MHW9 | An optimist believes we live in the best of all PGP Key: 0xDF1DD471 | possible worlds. A pessimist is sure of it!