Abstract: A sales data processor includes a connection unit to which a recording medium is connected. The recording medium has stored thereon access information for accessing a server device and identification information for identifying the sales data processor. A CPU of the sales data processor reads the access information and the identification information stored on the recording medium. And a communication unit of the sales data processor is authenticated by the server device based on the read access information and identification information, to communicate with the server device.

Abstract: A sales data processor connected to a server device via a communication network. A connection unit connects to the sales data processor a recording medium which has stored access information on the server device and identification information on the sales data processor. A CPU reads the access information and the identification information stored in the recording medium. A communication unit is authenticated by the server device based on the read access destination information and identification information to communicate with the server device.

Abstract: A sales data processing system wherein an upper limit value, a lower limit value, and a tax amount are entered into a tax amount list. The upper limit value and the lower limit value define a predetermined range of sales amounts, and the tax amount is determined based on a sales amount defined within the predetermined range. Difference values are calculated between a presently entered one of the upper and lower limit values and a previously entered one of the upper and lower limit values, and the calculated difference values are stored in accordance with a calculation order. A first difference value series not having regularity is judged, and a second difference value series having regularity repeated in a predetermined pattern from a series of the stored difference values is also judged.