Correction: read that * as "root mean square" i.e. square root of mean square of the deviations from the mean value.
---- Original message ---- >Date: Sun, 25 Jan 2009 22:09:29 -0600 (CST) >From: <[email protected]> >Subject: [USMA:42593] Odometer Precision and Accuracy >To: "U.S. Metric Association" <[email protected]> > > >Stan, > >Here is a further clarification of precision and accuracy. > >>From a set of measurements of the same quantity under the same circumstances, >>each measurement deviates from the mean value of the measurements, and the >>square root of the * mean of the deviations is called the standard deviation >>from the mean as a measure of the precision of the measurements. > >Whether an odometer *displays* decimal values to one, two, or three digits (to >an *apparent* accuracy of one meter) does not determine either precision or >accuracy of a measurement of distance by an odometer. > >A set of a reasonably large number of readings of the same distance by the >same odometer is necessary to determine the precision of the odometer (as >mounted in its carrier vehicle). > >The mean value of the odometer measurements (and its standard deviation) >compared with an independent measurement of the same distance (perhaps by a >laser device) then can be used as a measure of the comparative accuracy of the >odometer mean value of the distance. > >This may seem complicated, but these procedures are necessary to realize the >full requirements of precision and accuracy >with respect to an odometer. A single reading does not determine either >precision or accuracy. > >Gene. > >---- Original message ---- >>Date: Sun, 25 Jan 2009 18:50:45 -0500 >>From: "STANLEY DOORE" <[email protected]> >>Subject: [USMA:42568] Re: An Associated Press article in today's Atlanta >>Journal-Constitution >>To: "U.S. Metric Association" <[email protected]> >> >> Pat et al: >> >> Let's clarify the distinction between accuracy >> and precision. >> Two decimal place odometer readout is precision >> but it says nothing about how accurate that readout >> number is. >> Stan Doore >
