M1 Measurement (based on ISO 13655) is the only measurement condition that actively includes UV content in its calculations. This feature enables M1 to accurately record the true effect of OBAs in paper, whether in the production environment (D50) or the final evaluation environment (D65).

Using M1 ensures that the spectral data recorded by the instrument precisely reflects the color seen by the human eye under that specific standard light (including fluorescence). This measurement stability across different lighting standards is the only scientific method to eliminate ambiguity and ΔE error in OBA papers.