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That can't possibly right, though. No matter where I look, the math doesn't support it - using 1x7 galvanized, according to this page, and assuming an extreme load of 600 pounds, it would still only stretch by ~0.01% of the cable's length - which, for a cable of let's say 18 inches for measurement, has about the same stretch as it has diameter - a quarter inch. For stretch-proofed cable, this calculator (assuming eighth of an inch diameter, 18 inch long 1x7 cable and generous 120 pounds-force load) gives an even drastically insignificant stretch - 4 millimetres.

And unless they used slow, screw-gear actuators, I'm pretty sure that the inaccuracy is in similar numbers.