The -hp- Model 3552A Transmission Test Set is designed for use in testing telecommunications equipment. It provides calibrated test signals while simultaneously making frequency or level measurements on voice frequency systems, program systems and data circuits. Some of the features provided are dial and hold capabilities, input impedances of 150 Ω, 600 Ω, and 900 Ω, choice of four noise weighting filters and digital readout of level or frequency.