Usage Tips:Crack Monitor: The crack monitor consists of 2 plates with overlapping partial lengths. The bottom plate is calibrated in millimetres, the top plate is clear and marked with a crosshair cursor. Practical and convenient to use. Accurate: The crack monitor with highly clear acrylic plate allows easy to read and watch the data. The scale plate is designed with scale in both horizontal and vertical directions. The Indicator plate has crossed indicator lines design. Easy to Install: 2 plates can be easily fixed together without the need for glue or complicated installation steps. It is convenient and stable to use. Practical: The crack monitor can be used for monitoring cracks in walls and their evolution over the measuring time. Quality Acrylic: This crack monitor is crafted by quality acrylic, sturdy and enduring. And it is resistant to water; scratch and sun. Easy to install and reusable. Colour:As Shown Material:Acrylic Package Contents: 1set x crack monitor 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.