A device for measuring the length of a cable under tension moved through the device generally comprises a frame, a measuring pulley rotatably mounted on the frame; an anti-slip device for rollingly holding the midsection of the cable in a non-slipping manner against the measuring pulley such that movement of the cable rotates the measuring pulley, and a rotation sensor for sensing the rotation of the measuring pulley and producing a signal indicative of the rotation thereof. The anti-slip device generally comprises one or more loading rollers and a loading assembly including a flexible tension member for applying loading to the loading rollers such that movement of the cable rotates the measuring pulley. A location measuring device incorporating the cable length measuring device determines the direction and distance from the location measuring device to a free end of the cable.