Abstract: A communication system for transmitting accounting instructions has central and decentralized devices. Accounting instructions input by individual users at the decentralized devices are checked for authenticity and retransmitted to the central devices to be processed. According to the invention, the communication system has at least virtually networked devices, means of an independent second communication system (2) with stationary devices (21, 22/1, 22/2) and portable communication transmitters (23) which communicate therewith in an encrypted manner. The stationary devices (21, 22/1, 22/2) of the second communication system (2) may be at least temporarily connected to the central devices (11) of the first communication system (1). Accounting instructions given by individual users with the portable communication transmitters (23) of the second communication system (2) can be previously authenticated in one of the central devices (11) of the first communication system.