The flow sheet stimulates thought on matters of detail which might otherwise be missed and thus provides new ideas for avoiding difficulties. Against each critical point, list immediate steps which may be taken to reduce variation together with further ideas which could be adopted at a later stage to eliminate it completely. The success of any quality control system depends on the sympathetic interest of top management. The initiative system must come from the top management. It is useless merely to instruct a laboratory to start a quality control system unless management at all levels from Managing Director to shop foreman is prepared to accept it and to co-operate in its implementation.