Quantity: One Piece Net Weight: 20.6 grams Gross weight: 24.5 grams Pack size: 9.5 x 5 x 1.5 cm. Product size 9.5*4.5*1cm How to use the measuring instrument: When the wheel rolls between two points on the map, the pointer of distance measurement rotates accordingly, record the value according to the corresponding scale and multiply it by the scale factor to get the actual distance between the two points, which is more accurate than the straight line distance measured with a ruler. Many map rangefinders are convenient and quick to measure mileage distances and are designed to measure actual distances on curved routes on a map. Precautions: 1. Use in a horizontal state to ensure accuracy as much as possible; 2. In order to avoid the confusion of the magnetic needle, please keep a certain distance from barbed wire and magnetic objects when using it. 3. Do not hit the objects with a survey ruler, so as not to affect the measurement accuracy. 4. Disc surface and lens should be kept clean, do not wipe with cloth or dirty hands; 5. It should be closed when not in use and placed away from ferromagnetic substances to prevent loss of magnetism.