Apparatus for optimising the design of a manufacturing process in order to achieve predetermined goals including: A computer simulation model of the structural elements of a manufacturing process pre-programmed to operate according to predetermined flow and sequencing rules and data describing the required product mix and to output, during operation, data on request relating to breakdowns and queues at various resources within the process. A calculator received the data and calculates first values of complexity and constituent elements thereof from the output data of the computer simulation model and second values of complexity and constituent elements thereof from similar data relating to the real manufacturing process in operation. A comparator for receiving and comparing the said first and second values and for selecting improvement data in accordance with the result of that comparison from an improvement rules database and for providing said improvement data to said computer simulation model so as to cause a modification of the model.