Accuracy and errors

Abstract

Tests give rise to numerical results for properties such as modulus, flow stress etc. but quoting a result without an estimate of its accuracy is only of limited use. For example a specimen may be measured and its length quoted as 10 mm. Conventionally this may be taken to mean that the length falls between 9 and 11 mm i.e. the specimen length is 10±1mm. However the measurement may have been taken to either greater or lesser accuracy than convention suggests. It could have been measured to 0.1mm giving a result 10.0±0.1mm or alternatively taken very roughly as ‘about 10 mm’ meaning anything between 8 and 12 mm. If the accuracy is not quoted a user of the measurement is unaware of the measurement accuracy and can only guess that the measurement has been made to an accuracy of ± 1 in the last figure. It is common practice to call the accuracy estimate ‘the error’ and although this may carry the implications of ‘a mistake’ the terminology is commonly used and will be used here.