Features:* The bubble inside the circle will tell you that the tested surface is at the water level as the bubble in the exact center of the circle.* The surface of the tested materials can be adjusted to the water level as the bubble shows.* It will make your life more convenient.* Test level method : You need to find a completely horizontal plane, then place the product on the plane to test. You may know. If the product is accurate. If one side of the product is not even, you can rotate the other side 90 degrees to test. Technical data:* Product name: bubble level* Material: acrylic + plastic* Liquid color: green* Shape: round* Optional size(approx): A(10*6mm), B(12*7mm), C(15 *8mm), D(18*9mm)* Quantity: 5 pieces Package content: 5 x bubble level Note: 1. The real color of the item may be slightly different from the pictures shown on website caused by many factors such as brightness of your monitor and light brightness.2. Please allow slight manual measurement deviation for the data.