Accuracy-&-Precision(1)准确度,精确度

Accuracy&PrecisioninMeasurementAccuracy&Precision•Accuracy:•Howcloseyouaretotheactualvalue•Dependsonthepersonmeasuring•Calculatedbytheformula:%Error=(YV–AV)x100÷AVWhere:YVisYOURmeasuredValue&AVistheAcceptedValue•Precision:•Howfinelytunedyourmeasurementsareorhowclosetheycanbetoeachother•Dependsonthemeasuringtool•DeterminedbythenumberofsignificantdigitsAccuracy&Precision•Accuracy&Precisionmaybedemonstratedbyshootingatatarget.•Accuracyisrepresentedbyhittingthebullseye(theacceptedvalue)•Precisionisrepresentedbyatightgroupingofshots(theyarefinelytuned)Accuracy&PrecisionPrecisionwithoutAccuracyNoPrecision&NoAccuracyAccuracywithoutPrecisionAccuracy-Calculating%ErrorHowCloseAreYoutotheAcceptedValue(Bull’sEye)Accuracy-Calculating%Error•Ifastudentmeasuredtheroomwidthat8.46mandtheacceptedvaluewas9.45mwhatwastheiraccuracy?•Usingtheformula:%error=(YV–AV)x100÷AV•WhereYVisthestudent’smeasuredvalue&AVistheacceptedvalueAccuracy-Calculating%Error•SinceYV=8.46m,AV=9.45m•%Error=(8.46m–9.45m)x100÷9.45m•=-0.99mx100÷9.45m•=-99m÷9.45m•=-10.5%•Notethatthemeterunitcancelsduringthedivision&theunitis%.The(-)showsthatYVwaslow•Thestudentwasoffbyalmost11%&mustremeasure•Acceptable%erroriswithin5%remeasure-5%5%remeasure•Acceptableerroris+/-5%•Valuesfrom–5%upto5%areacceptable•Valueslessthan–5%orgreaterthan5%mustberemeasuredSignificantDigitsHowtoCheckaMeasurementforPrecisionSignificantDigits&Precision•Theprecisionofameasurementisthesmallestpossibleunitthatcouldbemeasured.•SignificantDigits(sd)arethenumbersthatresultfromameasurement.•Whenameasurementisconvertedweneedtomakesureweknowwhichdigitsaresignificantandkeeptheminourconversion•AlldigitsthataremeasuredaresignificantSignificantDigits&Precision•Howmanydigitsarethereinthemeasurement?•Allofthesedigitsaresignificant•Thereare3sdLengthofBar=3.23cmcm12340•Whatisthelengthofthebar?SignificantDigits&Precision•Ifweconvertedtothatmeasurementof3.23cmtommwhatwouldweget?•Right!32300mm•Howmanydigitsinourconvertednumber?•Aretheyallsignificantdigits(measured)?•Whichonesweremeasuredandwhichoneswereaddedbecauseweconverted?•IfweknowthesignificantdigitswecanknowtheprecisionofouroriginalmeasurementSignificantDigits&Precision•Whatifwedidn’tknowtheoriginalmeasurement–suchas0.005670hm.Howwouldweknowtheprecisionofourmeasurement.•Therulesshowinghowtodeterminethenumberofsignificantdigitsisshowninyourlabmanualonp.19.Thoughyoucanhandlethem,theyaresomewhatcomplex.