Error in Measurements - Error in Measurements The...

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Error in Measurements The difference between the actual value of a physical quantity and the measured value of the quantity is the error of the measurement. Quantitative measurements are measurements with which error can be associated. The amount of error associated with a particular measurement may be considered from the point of view of precision or the point of view of accuracy. The precision of a measurement expresses the error, or deviation, of the measurement from the average of a large number of measurements of the same quantity, while the accuracy of a measured value expresses the deviation of the measurement from the true value of the quantity. Error is considered from the point of view of accuracy when the true value is known, but when the true value of a quantity is not known precision must be used in place of accuracy. It is impossible to obtain accuracy if precision cannot be obtained, but precision does not guarantee accuracy. Any significant systematic error (an error which, for some systematic or determinate reason, influences the measurement in a known or knowable way) may give results which are very precise--and highly inaccurate. Scientists often obtain the precision of a measurement not by actually carrying out a large number of measurements but from knowledge of the limitations of the apparatus used to carry out the measurement procedure. The limitations of the apparatus available in an average basic chemistry laboratory used for undergraduate students are given in the Table below. These precisions can be obtained using proper measuring techniques and are a measure of the deviation expected in repetitive measurements.
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