Just guessing, they must feed a high frequency the cable is designed to carry through it. How well it transfers the frequencies it will need to carry. Reflections in it, and stuff that's too complicated for me to describe. Signal loss, capacitance, propagation speed, plus others? An ohmmeter itself would just check resistance without a frequency, and no other necessary measurements would be done using a basic ohmmeter. Just my guess.
Digital cable impedance question
I see that digital cables are rated at 75 ohms for RCA and 110 ohm for AES/EBU. How are these measurements taken? It seems to me that wire should have no resistance if it is a straight measurement from one end to the other. Anyone know how they got these figures? Thanks for reveiwing and replying.