A really great layman's introduction to accuracy and precision.
Accuracy and precision are not the same things. In the field of science and data, “accuracy” is typically considered to be a measure of how close a number is to that quantity’s true value. “Precision” is a term with two relevant meanings. The first describes the degree to which repeated efforts to do, or measure, something will produce the same results. The second meaning is a measure of the relative accuracy with which any given number can be represented, and is typically expressed through the use of “significant figures.”