The main function: Used for chartwork to draw lines indicating bearing or course, and to measure the degree or amount of bearing and course on nautical charts. Two hands each hold a ruler; alternately move them in parallel across the chart. Usage: During operation, apply slight pressure to keep one foot stationary while moving the other hand to push the movable foot. Alternate the movement of the two feet in parallel until the desired position is reached. This prevents displacement of the fixed foot. Size: 450mm Material: Plastic Color: White Package Contents: 1 x Chart parallel ruler Only the above items are included; other products are not included. Note: Lighting and different display settings may cause slight variations in color between the image and the actual item. Measurement may vary by +/- 1-3cm.