This handy tool used in networking provides feedback on a cable run to determine the physical distance of the cable or to help identify where a break is in a cable.

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Time-domain reflectometry (TDR) tests a cable by sending a short electrical pulse along the line and watching for reflections. If the line is perfect, the pulse returns cleanly; if there’s a break or impedance change, part of the pulse reflects back. By measuring how long the reflection takes to return and using the cable’s propagation speed, you calculate the distance to the fault. This makes TDR ideal for not only locating where a break is, but also measuring how much cable lies between ends.

A cable tester can check continuity and general faults but won’t provide precise distance along the run. A multimeter measures voltage, resistance, or current, not the location of a fault along a cable. A toner and probe helps identify which cable is in a bundle or behind walls, not the fault’s distance. So the tool that gives feedback on the length of the run and the exact fault location is TDR.