Industry is a basic category of business activity. Firms in the same industry are on the same side of the market, produce goods which are close substitutes and compete for the same customers. For statistical purposes, industries are categorized following a uniform classification code such as Standard Industrial Classification (SIC). Changes in the volume of the physical output of the nation's factories, mines and utilities are measured by the index of industrial production. The figure is calculated as a weighted aggregate of goods and reported in headlines as a percent change from previous months. It is often adjusted by season or weather conditions and thus volatile. However, it is used as a leading indicator and helps in forecasting GDP changes. Rising industrial production figures signify increasing economic growth and can positively influence the sentiment towards local currency.