By contrast, commercial washers for "internal" business operations (still often referred to as "washer/extractor" machines) may include features absent from domestic machines. Many commercial washers offer an option for automatic injection of five or more different chemical types, so that the operator does not have to deal with constantly measuring out soap products and fabric softeners for each load by hand. Instead, a precise metering system draws the detergents and wash additives directly from large liquid-chemical storage barrels and injects them as needed into the various wash and rinse cycles. Some computer-controlled commercial washers offer the operator control over the various wash and rinse cycles, allowing the operator to program custom washing cycles.