Features: *The bubble inside the circle will tell that the tested surface is in water level as the bubble in the exactly middle 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, and then put the product on the plane to test. You can know.if the product is accurate.If side of the product is not level, you can flip the other side at 90 degrees to test. Specifications: *Product Name: Bubble Level *Material: acrylic+plastic *Liquid Color: Green *Shape: Round *Optioanl size(Approx.): A(10*6mm), B(12*7mm), C(15*8mm), D(18*9mm) *Quantity: 5pcs Package Contents: 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.