Marine navigation ruler for nautical charts - accurate parallel tool for sailorsThe main role: Before Chartwork for drawing lines bearing line or course, the degree or amount of bearing line degree course line.<br> Two hands each holding a ruler of David, alternately moved in parallel.<br> 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.<br> size:600mm<br> Material:plastic<br> colour:White<br> Package Contents:<br> 1 * Chart parallel ruler<br> Only the above package content, other products are not included.<br> 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 +/- 1-3cm.