liuzengqiang:
Just thinking out loud, would measuring the resistance of the remaining wire help? If you have 30,000ft of wire, say 20 AWG, you have over 300 ohm of resistance. Maybe using a good multimeter with 4-wire sensing to get acceptable accuracy. ?
that means 100 ft =1 Ohm. I dont think anyone can trust a "1 Ohm" measurement for this purpose.
But afaik most cable companies have markings per "meter" (EU) of cable length. I really couldn t believe there is a problem with this...
liuzengqiang:
What is your expected accuracy anyway?
yes, that s a good Q.