The maximum flexibility required is equal to the coincidence of a maximum decrease of wind output with a maximum increase of demand. This flexibility measure has to be compared to the maximum flexibility available, which is determined by the maximum ramp rate of controllable technologies times their availability and capacity. The flexibility margin indicator compares the maximum flexibility available with the maximum flexibility required, in proportion to the maximum flexibility required (ECOFYS, et al., This measure does not account for alternative sources of system flexibility like interconnection capacity, demand response and storage. The indicator warrants the use of assumptions for maximum ramp rates of controllable technologies. The difficulty is to take into account differences in plant availability, i.e. whether the plant is already (partially) used in the system or not, and therefore whether the plant has to ramp from a cold or warm state with corresponding ramping times.