An apparatus includes a drum to draw in or let out a line and a motor and transmission coupled to the drum to apply a torque thereto. A power sensor measures an amount of current drawn and/or voltage supplied to the motor as the motor applies torque to the line. A processor calculates an amount of weight that is attached to the line based on the amount of power consumed by the motor. Alternatively, if the motor is operated in generator mode, a current sensor may measure an amount of current generated by the motor and the processor may calculate an amount of weight that is attached to the line based at least partly on an amount of current that is generated by the motor.