23rd June will go down in history as a very difficult day in Westminster - Brexit Day. Nonetheless, Andrew Darnton and Andrew Harrison boldly produced an engaging and thought provoking complexity seminar in Whitehall and we thank them wholeheartedly for a superb event. The seminar topic was 'Revaluation: Measuring Paradigm Shift'. 'Revaluation', a new innovative method for measuring change in complex systems, was presented and discussed. Revaluation comes out of a year's work evaluating 'bottom-up' change within the NHS. It is an approach based on participative methods, in which evaluators and evaluated are equal actors in a system of measurement, designed to reveal the ‘full value’ of the change intervention or movement. Since its evolution in the ‘messy’ system of the NHS, Revaluation has been applied to the challenge of tackling biodiversity, and to repositioning the public arts. Notes from this seminar are listed below.