1.Small, and portable.Professional Multi-function High Precision On-board Compass. 2.Great for marine, vehicle, boating, traveling, hiking, outdoors, etc.The outer tick of outer ring is CM ruler. The pointer rotating a week is a cm. 3.The inner tick of outer ring is 1: 50,000 scale, applying to the 1:50,000 map. 4.The outer tick of inner ring is 1: 20,000 scale, applying to the 1:20,000 map. 5.The inner tick of inner ring is 1:5,000 scale, applying to the 1:5,000 map. Instruction: Move the pointer to zero, . at the scale of 1:1. Align the small wheel to the measuring address, slip(rolling) to the destination along the route. According to the map scale, read the number of kilometers on the odemoter. Material: Aluminum alloy + ABS colour: black Package Contents: 1 x Map Rangefinder Odometer 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.