A tariff arrangement which is preferably intended for an electricity meter comprises a microprocessor, a data memory and a bidirectional interface for transfer of data with a read-out device. For the duration of a data transfer operation a timing member is activated and by way of a logic circuit inhibits a predetermined memory region to prevent data from being written thereto. The data which are stored in the memory region, for charging purposes, are therefore protected from unintentional alterations during the data transfer operation, even if the software should have corresponding defects. The function of the timing member and the logic circuit can be checked in a simple manner.