Abstract: Apparatus is described for testing a telephone line between a customer's telephone and a local exchange associated therewith. The apparatus comprises a field unit positioned between the customer's telephone and the line, an exchange unit positioned at the exchange, and a microcomputer associated with the field unit for controlling operation of the field unit and the exchange unit. The field unit and the exchange unit each have means for transmitting frequency tones down the line and means for measuring the voltage across the line. The microcomputer is programmed to calculate the loudness rating of the line from the measured voltage values.