The main role: Before Chartwork for drawing lines bearing line or course, the degree or amount of bearing line degree course line.Two hands each holding a ruler of David, alternately moved in parallel.Usage: When the move operation, the appropriate force to suppress static hand foot, one hand pushing moving feet, two feet alternately moved in parallel until the required position. Alternately moving, to prevent the static foot displacement.size:450mmMaterial:plasticcolour:WhitePackage Contents:1 * Chart parallel rulerOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is + 13cm.