Precision and accuracy are two aspect of certainty with which we are particularly concerned about in quantitative analysis. Precision, or reproducibility, refers to how close the measurements in a series are to each other. Accuracy refers to how close a measurement is to the real value. There are two common types of error, random and systematic , an analytical chemist must work to eliminate in order to achieve the goal of precise and accurate quantitative analysis.
Random error produces individual values that are both higher and lower than the average value.
Such error always occurs, but its size depends on the scientist's skill and the instrument's reproducibility. The contribution of random error to the final result can often be reduced by averaging a large number of measurements. When making a measurement in analytical chemistry, you are generally trying to determine some property of your sample. In this course, that property is usually the quantity of the analyte in the sample. Because of random errors associated with the measurement, the result of any single trial might not be an accurate representation of the true value.