This report runs through the CART principles (= Credible, Actionable, Responsible, and Transportable) which aim to improve monitoring and evaluation (M&E) systems. Like in the Goldilocks fairy-tale, where a girl finds a home of three bears and things are either too big, too small or just right, the CART principles support social enterprises to collect the right data that corresponds exactly to their needs. The case study examines the theories of change and measurement strategies for two investments of the impact investor organisation Acumen.