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 of data. The scale plate includes markings in both horizontal and vertical directions. The indicator plate has crossed lines for precise measurement. Easy to Install: The two plates can be securely fixed together without glue or complex installation 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, resistant to water, scratches, and sunlight. Easy to install and reusable. Color: As shown. Material: Acrylic. Package Contents: 1 set x crack monitor. Note: Light reflection and display differences may cause slight variations in color between the image and the actual item. Measurement allowance is +/- 1-3 cm.