An error which arises if the two beams in a double-beam
spectrometer are not fully equivalent in transmitted
power nor are corrected to be so (e.g. due to unmatched cells).
Source:
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