Method of Application : 1. First , put the vertical ruler in a vertical position , tighten the screw ,and place the insulating plate on the track surface， make the two measuring heads fit closely to inner side of the track .Then open the vertical ruler studdle to absorb the magnet and adjusting screw,Loosen the frame to tighten the screw , pull the horizontal ruler to make the left side of platform supporting seat fit to the edge of the platform , Make the platform studdle fit platform plane ; slide the vertical ruler till the horizontal bubble is in the center.Tighten the frame and the screw . 2. The marking value of the magnifying glass on the red line is the distance from the track center to the edge of the platform, the value of the vertical ruler “0”is the distance from track surface to platform plane . 3. After the measurement completed ,put platform studdle into the supporting seat , loosen the screw to absorb the vertical ruler with the magnet .