Oooooooh ................ forgot about this nugget.
Only perused page 1 and hopefully found one I can add to the 'C' menu ............. one which is used daily by OR is CIDT (Copper Integrated Digital Test).
I'm sure Mr Cat would be able to word it better than I, and I am off to work very shortly ...... but this basically runs a low-frequency test of the copper pair, followed by a digital test by pinging the EU's router at various frequencies. Very helpful in detecting high resistance (HR) faults.
Also ...... 'Battery Contact' could be better worded to, 'Where one telephone circuit is in contact with another. The affect on service depends on the severity of said contact, which can be anything from a few volts up to the full working voltage of circa -50v'.
I'm gonna stop now.