Determine longitude on protractor to determine course or bearing The protractor's vertex allows placing a dividing point or pencil on a point of the hole A string can be used to fix the stopwatch used on the hole for a long distance of course. When charting, it is used to draw the bearing line or heading line, and measure the bearing line or heading degree. colour:Transparent Material:plastic size:300mm Package Contents: 2*Nautical chart drawing triangle ruler Only 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 +/- 1-3cm. The protractor's allows placing a dividing point or pencil on a point of the hole A string can be used to fix the stopwatch used on the hole for a long distance of course. When charting, it is used to draw the bearing line or heading line, and measure the bearing line or heading degree. Determine longitude on protractor to determine course or bearing