The HP Agilent 3550B Portable Test Set iss designed specifically to measure transmission line and system characteristics such as continuity and attenuation distortion. It is particularly usedful for lineup and maintenance of multi-channel communication systems. Model 3550 B contains a wide range oscillator, a voltmeter, and a patch panel to match both oscillator and voltmeter to 135, 600, and 900 ohm lines.