QUANTITATIVE ANALYSIS - Error, Accuracy and Precision

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The error of a measured value is the numerical difference between it and the true value.
E = Absolute error
T = True value
O = observed or measured value
E = O – T
The accuracy of a determination may be defined as the agreement between measured value and the true or most probable value. It is the value of E compared to T that is of importance. Errors are usually expressed in percent (E/T × 100). Smaller the error, greater the accuracy. Accuracy expresses the correctness of a measurement.

The precision of a measurement means the reproducibility or the extent of agreement of the individual values among themselves. The magnitude of the difference between individual values and the arithmetic mean of all is a measure of the precision.
The smaller the difference the greater the precision.