Accuracy

Errors in experiments stem from incorrect design, inexact equipment, and approximations in measurement. Imperfections in equipment are a fact of life, and sometimes design imperfections are unavoidable as well. Approximation is also unavoidable and depends on the fineness and correctness of the measuring equipment. For example, if the finest marks on a ruler are in centimeters, then the final measurement is not likely to have an accuracy of more than half a centimeter. But if the ruler includes millimeter markings, then the measurements can be an order of magnitude more accurate.

Accuracy differs from precision. Precision deals with how repeatable measurements are—if multiple measurements return numbers that are close to each other, then the experimental results are precise. The results may be far from accurate, but they will be precise.