the economy. Form of allocation The economist Ross Garnaut states that permits allocated to existing emitters by 'grandfathering' are not 'free'. As the permits are scarce they have value and the benefit of that value is acquired in full by the emitter. The cost is imposed elsewhere in the economy, typically on consumers who cannot pass on the costs. Market and least-cost Some economists have urged the use of market-based instruments such as emissions trading to address environmental problems instead of prescriptive "command-and-control" regulation. Command and control regulation is criticized for being insensitive to geographical and technological differences, and therefore inefficient; however, this is not always so, as shown by the WWII rationing program in the U.S. in which local and regional boards made adjustments for these differences. After an emissions limit has been set by a government political process, individual companies are free to choose how or whether to reduce their emissions. Failure to report emissions and surrender emission permits is often punishable by a further government regulatory mechanism, such as a fine that increases costs of production. Firms will choose the least-cost way to comply with the pollution regulation, which will lead to reductions where the least expensive solutions exist, while allowing emissions that are more expensive to reduce. Under an emissions trading system, each regulated polluter has flexibility to use the most cost-effective combination of buying or selling emission permits, reducing its emissions by installing cleaner technology, or reducing its emissions by reducing production. The most cost-effective strategy depends on the polluter's marginal abatement cost and the market price of permits. In theory, a polluter's decisions should lead to an economically efficient allocation of reductions among polluters, and lower compliance costs for individual firms and for the economy overall, compared to command-and-control mechanisms. Measuring, reporting, verification and enforcement Assuring compliance with an emissions trading scheme requires measuring, reporting and verification (MRV). These measurements are reported to a regulator. For greenhouse gases, all trading countries maintain an inventory of emissions at national and installation level; in addition, trading groups within North America maintain inventories at the state level through The Climate Registry. For trading between regions, these inventories must be consistent, with equivalent units and measurement techniques. In some industrial processes, emissions can be physically measured by inserting sensors and flowmeters in chimneys and stacks, but many types of activity rely on theoretical calculations instead of measurement. Depending