Patent ID: 7760369

Claim:
An apparatus for determining an elevation of a working tool relative to a reference plane, comprising: a rotary laser system emitting a rotating laser beam that spans upon rotation a plane inclined relative to the reference plane by an inclination angle, the rotary laser system comprising a first radio unit; a detector mounted on the working tool for detecting the laser beam, the detector comprising a second radio unit, wherein the detector is adapted to initiate a distance measurement to determine the distance between the working tool and the rotary laser system when the detector is hit by the rotary laser beam; wherein during the distance measurement the detector is adapted to control the second radio unit to transmit a radio signal, the rotary laser system is adapted to control the first radio unit to transmit a return radio signal in response to receiving the radio signal from the detector, and the detector is adapted to receive the return radio signal from the rotary laser system, to measure an elapsed time between the transmission of the radio signal and reception of the return radio signal, and to determine the distance between the working tool and the rotary laser system on the basis of the elapsed time, wherein the detector is adapted to determine the elevation of the working tool on the basis of the inclination angle and the determined distance between the working tool and the rotary laser system.