Different forms of economic planning have been featured in various models of socialism. These range from decentralized-planning systems which are based on collective decision-making and disaggregated information to centralized systems of planning conducted by technical experts who use aggregated information to formulate plans of production. In a fully developed socialist economy, engineers and technical specialists, overseen or appointed in a democratic manner, would coordinate the economy in terms of physical units without any need or use for financial-based calculation. The economy of the Soviet Union never reached this stage of development, so planned its economy in financial terms throughout the duration of its existence. Nonetheless, a number of alternative metrics were developed for assessing the performance of non-financial economies in terms of physical output (i.e. net material product versus gross domestic product).