For Cable-Driven Parallel Robots, the cable length is the only element we control. Better knowledge of this parameter will improve robot performances. We propose a new cable length autocalibration subsystem. It consists of an instrumented cable, inductive sensors and a controller for digital data processing. Cable would be instrumented by metallic marks, with variation in distance between successive marks. Inductive sensors will allow the detection of metallic marks; it will be placed vertically on the support, with variation in distance between successive sensors. Each detection will correspond to a cable length. By analyzing the succession of cable lengths detected at particular moments, we can identify our position on the cable, then deduce its length. A closed-loop autocalibration may allow continuous cable length adjustment.