This approach is based on the concept that most items of revenue and expense within a hotel have a fixed component, which does not vary with a hotel's occupancy or other volume measure, and a variable component, which changes in direct relationship with occupancy or another measure of volume (e.g., total revenue). By estimating the food revenue for a specific level of occupancy and knowing what portion of the revenue is fixed and what portion is variable, the appraiser can calculate the revenue for other different levels of occupancy.