In the 1960s, the Swiss company SODECO S.A. introduced the TL 1601-1 analog call unit indicator. Based in Geneva, the company was active in the fields of industrial meters and pulse totalizers. It consists of two analog registers (using mechanical relays, like those in old odometers): the upper one tallies the total number of telephone units used, while the lower one tracks the units for a single call. Two buttons—one red and one white—are located on the top of the device to reset the displays. The device connects to the telephone network at the rear. It is made of dark gray plastic. A label on the base of the device displays the model, the company name, and the billing pulse frequency. Its dimensions are 7 cm x 11 cm x 9 cm. The sole customer for these devices was the Hellenic Telecommunications Organization (OTE S.A.), which managed the public telephone network.