The Federal Reserve's monthly index of industrial production and the related capacity indexes and capacity utilization rates cover manufacturing, mining, and electric and gas utilities. The industrial sector, together with construction, accounts for the bulk of the variation in national output over the course of the business cycle. The production index measures real output and is expressed as a percentage of real output in a base year, currently 2007. The capacity index, which is an estimate of sustainable potential output, is also expressed as a percentage of actual output in 2007. The rate of capacity utilization equals the seasonally adjusted output index expressed as a percentage of the related capacity index.