A number of measured values (x 1 , x 2 , ... x i , ... x n) equivalent to each other with respect to statistical considerations, e.g. the results of repeated analyses using only one analytical method on a substance that is presumed to be homogeneous.
Sources:
Orange Book, 2nd ed., p. 4 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1994, 66, 595. 'Nomenclature for the presentation of results of chemical analysis (IUPAC Recommendations 1994)' on page 597 (https://doi.org/10.1351/pac199466030595)