The telephone unit meter was a device used in telephone exchanges to record 16 kHz billing pulses. Connected to the telephone line, it recorded the pulses—factoring in both the duration and distance of a call—and displayed the billing units (e.g., 1 unit for a local call). It consists of an analog panel—featuring a mechanical counter similar to those found in old odometers. It was used in OTE S.A. telephone exchanges to record usage units; the billing department would then convert these into costs and mail the bills to subscribers every two months. Today, it too has become a piece of telecommunications history.