That mass of analyte which produces an integrated absorbance signal whose net area is equal to 0.0044 s.
Source:
PAC, 1992, 64, 253. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - XII. Terms related to electrothermal atomization (IUPAC Recommendations 1992)' on page 258 (https://doi.org/10.1351/pac199264020253)