Crack Monitor: The crack monitor consists of two plates with overlapping partial lengths. The bottom plate is calibrated in millimeters, and the top plate is clear with a crosshair cursor. Practical and convenient to use. Accurate: The crack monitor features a highly clear acrylic plate for easy reading and observation. The scale plate includes markings in both horizontal and vertical directions. The indicator plate has crossed lines for precise monitoring. Easy to Install: The two plates can be easily fixed together without glue or complicated steps. Convenient and stable during use. Practical: This device is suitable for monitoring cracks in walls and tracking their development over time. Quality Acrylic: Made from durable acrylic material, the crack monitor is sturdy, water-resistant, scratch-resistant, and UV-resistant. Easy to install and reusable. Color: As shown Material: Acrylic Package Contents: 1 set x Crack Monitor Note: Light reflection and differences in display screens may cause slight variations between the color of the item in the image and the actual product. Measurement error allowance is +/- 1-3 cm.