DATA RECORDING MACHINE

A cash register with a keyboard (31), journal printer (47) and a check slip printer (32) is controlled by a microprocessor system with a CPU (102), a program ROM (105) and a RAM (106) including various registers for storing running totals of various types. The printer (32) prints till receipts and end-of-day check slips authenticating non-rigged operation of the cash register. Thus, each time such a check slip is printed a fresh bit of an EPROM memory (106) is set from 1 to 0 under control of a register (181) and a pulser circuit (191), the EPROM being fixed non-removably to the machine and shielded aginst UV erasure. The printed check slip includes the serial number thereof as represented by the EPROM contents, a special symbol identifying a non-manipulatable machine and the machine number recorded in a section (161) of the EPROM. In a modified embodiment the EPROM is replaced by a counter, e.g. a mechanical counter, which can only be incremented (and cannot be decremented or zeroized). The counter is incremented each time a check slip is printed and the number in the counter is included in the printout. Check slips with unbroken series of check slip numbers provide evidence of non-rigged operation.