The crack measuring instrument is made of high-quality acrylic material, which is strong, smooth, wear-resistant, and not easy to break. Designed with highly transparent acrylic panels and easy-to-read measurement grids, the crack monitors are clear and precise. This tool can be used to monitor the horizontal or vertical movement of cracks on a flat surface. It supports 2D manual crack monitoring applications and is suitable for monitoring wall cracks and their development over time. The base plates of the crack measurement tools are calibrated in millimeters. It also features a transparent top plate marked with a cross-shaped thin line cursor. Material: Acrylic Color: Transparent Package Contents: 3 x Crack Measuring Instruments Note: Light reflection and different displays may cause the color of the item in the picture to appear slightly different from the real thing. The measurement allowed error is +/- 1-3 cm.