A study of the parameter trade-offs is so application dependent that an exhaustive treatment. The realization of a functional design is obviously a complex process requiring consideration of numerous interdependent parameters and evaluation of the resulting design trade-offs. The driving factor is, of course, the type and quality of scan line that is required for the particular application under development. Point-of-sale scanners have been with us for almost a decade and are gaining rapidly in acceptance by both the merchant and the customer. The design of a scanner subsystem requires consideration of numerous interrelated parameters that determine both performance and implementation. The scanner disk is 195 mm in diameter and consists of a sandwich of two identical glass disks encapsulating the holographic recording medium. The Fujitsu holographic point-of-sale scanner, FACOM 3721A, also uses a disk configuration to provide deflection, focusing, retrocollection scanning, and ambient light rejection.