Abstract: A portable microprocessor controlled transmission impairment measuring unit capable of operating as a master unit or a slave unit and responsive to digital or manual control measures all basic parameters necessary to characterize a voice channel for its ability to transmit data traffic, as defined by Bell System Technical Reference PUB41009, dated May 1975. Measurements can be made manually end-to-end with a unit at each end of a circuit to be tested; manually looped-back with a unit at one end of the circuit; or remotely from one end with a MASTER operated unit controlling a SLAVE operated unit with all measurements displayed on the MASTER unit. The unit can also be used as a voice frequency repeater and can be operated with other test sets and computers having compatible measurements and capabilities.All measurements are displayed on digital readouts. Two separate readouts allow simultaneous display of up to two different parameters.