Testing Analog Phone Line Voltage and Line Current with a Butt Set

One of the most valuable instruments used in telecommunications technology these days is the butt set. This extraordinarily handy little tool looks very much like a standard telephone handset that might be used to scan bar codes in a warehouse to record inventory transactions. However, in telecommunications applications, this useful and very versatile tool is instead used to detect opens and shorts, as well as for the detection of noise and transmission loss, and a wide range of other voice line problems.

Source: Blog.T3innovation.com