The gauges consist of two overlapping plates. The bottom plate is calibrated in millimeters, while the top transparent plate has a hairline cursor in the form of a . This design enables accurate monitoring of cracks. The monitors come with a redesigned fixing column that easily connects the two pieces without the need for glue. This ensures a secure and hassle-free installation. Made from polymer, the monitors are waterproof, sunlight , wear-, and scratch-. The highly transparent plastic sheet provides a clear and precise measurement grid. These monitors are specially designed to monitor cracks in walls and track their evolution over time. Keep track of wall deformation and changes with the included monitoring sheet. 1 mm(0.04inch) tick marks on X-Y axes;0.5 mm(0.02inch) discrimination 20 mm(0.79inch) horizontal and10 mm(0.38inch) vertical range The bottom plate is calibrated in millimetres and the top plate is transparent and marked with a hairline cursor in the form of a . The redesigned fixing column can easily fix the two pieces together without the need for glue. Crack monitoring scale is used to monitor the cracks in the walls and how they evolved along the measured time.High-quality polymer with easy-to-read measurement grid Use: can be used to monitor wall deformation/cracks Colour:As Shown Material:plastic Package Contents: 2 pairs x monitors 8 x screws 2 x monitor sheets Only the above package content, other products are not included. Note: Light reflection 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.