A postage metering system includes a keyboard; a display; a device for receiving an external smart card; a print module for printing a postal indicia; an accounting module for accounting for the value of each postal indicia printed; a microprocessor including a clock chip which generates pulses on a periodic basis, at least one register having contents which are indicative of a real time, first structure for automatically updating the contents of the register based on the number of clock pulses generated, second structure for permitting resetting of the contents of the register by a user via the keyboard to indicate a new real time, third structure for detecting whether the external smart card has been inserted in the receiving means, for determining whether the inserted external smart card is a real time clock security card, and for inhibiting operation of the second structure such that a user cannot reset the contents of the register to be indicative of the new real time unless the third structure determines that a real time clock security card has been inserted into the receiving device.