There are at least half a dozen whiteness indices in use today, and a similar number of legacy whiteness indices no longer in use. There are subtleties among them and it is important to know the forms of these whiteness metrics and conditions for which they are derived for. In general, a material will exhibit high whiteness if the material reflectance has high and even reflectance, near 100%, across the visible spectrum.
To communicate color values effectively, completely specify the 6 parameters of your measurement method and verify that your color measurement is repeatable. These are the key factors to ensure inter-instrument agreement.
The best inter-instrument agreement in color measurement at multiple locations occurs when a product is measured with the same instrument model from the same manufacturer combined with the same measurement method at all sites.