The first conveyorized automatic car wash appeared in Hollywood, California in 1940. Conveyorized automatic car washes consist of tunnel-like buildings into which customers (or attendants) drive. Some car washes have their customers pay through a computerized POS, or point of sale unit, also known as an "automatic cashier", which may take the place of a human cashier. The mechanism inputs the wash PLU into a master computer or a tunnel controller automatically. When the sale is automated, after paying the car is put into a line-up called the stack or queue. The stack moves sequentially, so the wash knows what each car purchased. After pulling up to the tunnel entrance, an attendant usually guides the customer onto the conveyor. At some washes, the system will send the correct number of rollers automatically, based on tire sensors. The tire sensor lets the wash know where the wheels are and how far apart they are. On other systems the employee may guide the customer on and press a 'Send Car' button on the tunnel controller, to manually send the rollers which push the car through. Prior to entering the automated section of the wash tunnel, attendants may prewash customers' cars. The car wash will typically start cleaning with chemicals called presoaks applied through special arches. CTAs, or "chemical tire applicators," apply specialized formulations, which remove brake dust and build up from the surface of the wheels and tires. In some car washes, the presoak application is followed by an empty space or idle zone. Wheel cleaning equipment, such as sill brushes or high-pressure wheel blasters, may be placed in the idle zone. A sill brush (also known as a wheel brush or tire brush) consists of an 8-foot-long brush assembly that is pushed against the car's wheels and door sill area. Brushes typically use flagged bristle, as dirt is usually most heavily concentrated on the lower parts of the car. The material on a sill brush may have alternating lengths or use a material that is intentionally mounted off-center to allow wheel surfaces of various depths to be cleaned. Sill brushes rely on the rotation of a customer's car's wheels in order to achieve complete wheel contact. Similar to the CTAs, wheel brushes often only activate when the customer buys a wheel cleaning upgrade. Some car washes use wheel-rim disc brushes in addition to or in place of sill brushes. These assemblies extend out towards the wheel and follow it at the same speed as the conveyor while rotating at high speeds to clean the wheels. At the end of a car wash's presoak idle zone is often a high-pressure arch that directs water at a vehicle's surface. Mitters are ribbon-like components that suspend cloth strips or sheets over the tunnel while utilizing motion to increase friction against the car's surface. The friction zone may also include specialized front grill and rear brushes. Older automatic washes - a majority of which were built prior to 1980 - used to use brushes with soft nylon bristles, which tended to leave a nylon deposit in the shape of a bristle, called brush marks, on the vehicle's paint. Many newer facilities use either a soft cloth or a closed-cell foam brush, which does not hold dirt or water, thus is less likely to harm the painted finish. After the main friction zone, some car washes have a dedicated care zone. Prior to entering the care zone, the car is rinsed with fresh water. This is immediately followed by a series of extra services. In many car washes, the first of these services is a polish wax. After the polish wax application is typically a retractable mitter or top brush and, in some cases, side brushes or wrap-around brushes. Next is a protectant, which creates a thin protective film over a vehicle's surface. Protectants generally repel water, which assists in drying the car and aiding in the driver's ability to see through their windshield during rain. A low-end wax or clear coat protectant follows the main protectant. A drying agent is typically applied at the end of the tunnel to assist in removing water from the vehicle's surface prior to forced air drying. After the drying agent, there may be a "spot free" rinse of soft water, that has been filtered of the salts normally present, and sent through semi-permeable membranes to produce highly purified water that will not leave spots. Dryers may be present in a variety of forms, such as stationary gantries with a contouring roof jet or as small circular assemblies with nozzles of various shapes and sizes mounted on arches. Mitters, side brushes, top brushes, and/or wraps outfitted with chamois- or microfiber-based material may follow the dryers. At "full-service" car washes, the exterior of the car is washed mechanically, by hand, or using a combination of both, with attendants available to dry the car manually and to clean the interior. Many full-service car washes also provide "detailing" services, which may include polishing and waxing the car's exterior by hand or machine, shampooing, and steaming interiors as well as other services to provide thorough cleaning and protection to the car.