Abstract: Devices configured to measure a length of rope moving through the device are disclosed. The devices of the present invention employ a sheave mounted for rotating within a housing. A rotation measuring assembly may determine the number of rotations of the sheave, and, thus, information about the length of the rope passing through the device. Information such as net rope length, gross rope length, current rope speed, maximum rope speed, or total rope length displaced during a certain period may be determined and displayed. A signaling device is configured to communicate the information.