Such classifications may omit crops that are extremely important in financial terms but which only occupy a small area, as it is land use rather than other aspects of production that is usually being considered. However, conversions may be applied to convert crop areas into measures of labour input (e.g. standard man-days) so that low labour intensity crops covering large areas, such as permanent pasture or extensive production of cereals, do not automatically appear as the dominant element within a crop combination. It is pos-sible to use gross margin and gross output data as conversions, but this usage is generally restricted by lack of readily available information.