Abstract: 1050 A. Units

Standard Methods uses the International System of Units (SI).¹ Quantities of mass and volume resulting from measurements and analyses are used to calculate and report concentrations of chemical and physical constituents in water. Concentration values must be reported using a unit of expression that is appropriate for the intended use of the data and within an appropriate value range for the unit expression used. For example, a typical unit expression for concentration is milligrams per liter (mg/L) where numerical values range from 0.1 to 999.9 mg/L. If the concentration value is less than 0.1, it is customary to express the concentration as micrograms per liter (μg/L) and if greater than 999.9, then express as grams per liter (g/L), with the numerical values adjusted accordingly. Record and report all measured and analytical results to the proper number of significant figures (see 1050 B).