
 Direction of leading line Sevastopol'skiy (54 deg 38.3 min N 20 deg 00.6 min E) axis is assigned by synchronized scanning of laser beams of N and S light beacons. When vessel is moving along leading line axis the laser beams are seen as two simultaneous flashes. When vessel shifts from leading line axis the laser beams are seen at different times as two sequential flashes.