the apparatus is a device that measures the attenuation effects of a telephone circuit &# 39 ; s physical construction , electrical characteristics , and equipment with respect to a series of waveforms at different frequencies , then combines the resultant values to create and display a reference number called the vasquez number , a unitless number that , once generated , becomes a representative signature of the circuit under test . this number can then be employed to compare ostensibly identical circuits , to identify aberrations indicative of wiretaps or other unauthorized equipment , or to monitor the circuit over time to determined whether such additional devices have been added .