This part of IS0 105 specifies an instrumental method for assessing the change in colour of a test specimen in comparison to an identical untreated reference, and the calculations undertaken to convert the instrumental measurements into a grey scale rating. This method is intended as an alternative to the many national methods for visual evaluation of the effect of a colour fastness test on any textile material. NOTE 1 There may be a difference between instrumental and visual assessments of specimens due to fluorescence, and/or other factors.