A procedure where the concentration of a known analyte may be determined by diluting the sample with solvent until the absorbance matches the absorbance of the analyte in the reference cell. This method is particularly useful if the Beer-Lambert law does not hold.
PAC, 1988, 60, 1449. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988)' on page 1456 (https://doi.org/10.1351/pac198860091449)