Measure the user experience

User experience or UX has for several years occupied a central role in value proposals of agencies, digital service providers and publishers. Made popular in the 1990s by Don Norman, the expression is today often overused, according to him. Our suggestion will be to (re-)propose a prescriptive definition of UX (iso standard 9241-210) and to demonstrate how this interfaces between the expression of need (client or user) and the ROI (return on investment). We thus defend the idea that UX is a determining factor in ROI. Using real examples gleaned from our own experience, we will show how it is possible to measure user experience and to thus assure our clients that a UX design operation is an investment that will bring immeasurable benefits.