An assay is an investigative (analytic) procedure in laboratory medicine, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence or amount or the functional activity of a target entity (the analyte). Qualitative assay, i.e. assays which generally give just a pass or fail, or positive or negative or some such sort of only small number of qualitative gradation rather than an exact quantity.
The average fixed cost (AFC) curve will decline as additional units are produced, and continue to decline. The average total cost (ATC) curve initially will decline as fixed costs are spread over a larger number of units, but will go up as marginal costs increase due to the law of diminishing returns.
Total cost is variable cost and fixed cost combined. Now divide total cost by quantity of output to get average total cost. Average total cost can be very handy for firms to compare efficiency at different output or when adjusting different factors of production.