Facsimile machines transmit a document's image to a remote location where it is printed on special paper by other facsimile machines. Each has a transmitter, a receiver, and a telephone in an acoustic coupler, which couples audible signals into and out of the telephone handset. Facsimile systems are expensive to acquire and can be expensive to operate; they should only be used in situations requiring unusual speed, security, or ease of delivery. Although law enforcement agencies can transmit arrest records and warrants on business convenience and other low-priced machines, fingerprints usually require better gray-scale reproduction and spatial resolution. The Institute of Electrical and Electronic Engineers' Facsimile Test Chart is the best-known test of facsimile quality; the guide explains its applications to texts, continuous-tone documents, and fingerprints. Facsimile machines can function as teletype or computer printers for text and graphics; mobile units can be installed in police cars. The report includes equipment selection criteria, photographs, diagrams, nine references, and a list of manufacturers.