There is no one Whiteness formula. ChromaChecker supports 

CIE Whiteness (D50/2°) 

This formula can be measured using various M-conditions - for substrates that contain OBA - the result depends on the selected measurement conditions (M0- M3).

Important note for X-Rite Exact users

• be sure to select the same M-conditions!
• setup proper formula   (My Default Settings/Function Defaults/Function Setting/Paper indices. Select "Whiteness E-313-05" (displayed on the screen as W-E-05)

There may be slight differences due to some differences in data rounding and the types of illuminators and observer definitions.