Repeatability refers to the degree of agreement of results when conditions are maintained as constant as possible with the same analyst, reagents, equipment, and instruments performed within a short period of time. It usually refers to the standard deviation of simultaneous duplicates or replicates, sr. It is the best precision that will be exhibited by a laboratory but it is not necessarily the laboratory’s typical precision. Theoretically the individual determinations should be independent but this condition is practically impossible to maintain when determinations are conducted simultaneously and therefore this requirement is generally ignored.