In the non-optical domain, that used to be a feature in the most expensive cable measuring gears (to the tune of €25k about 20 years ago). I had the pleasure o

In the non-optical domain, that used to be a feature in the most expensive cable measuring gears (to the tune of €25k about 20 years ago). I had the pleasure of using one of the devices that had that when I wired my old house. Borrowed the kit from ... an institution that allowed me to get their gear for a weekend. (Yes, I knew people in there.) Having the device tell me that a given strand in a CAT5e cable was faulty at <this many meters> from my location made it surprisingly easy to detect where I'd messed up.