Easy to use, just put the metal wheel on the map and roll it, the would point to the precise scale. metal and for shell of map , for tough, wear-resistant, rainproof and Lightweight and portable, with a metal replacement for easy holding. This rangefinder allows you to quickly calculate distance by measuring the distance between two points on the map. A nice replacement people who love outdoor activities like hiking, traveling, backpacking,, Manufacturer: Navna