Principle of optical imaging: The image is not projected onto the paper. Through the lens paper, you can see the image on the drawing. The trackpad has two sides, front and back, and the projection effect is different on both sides. Please use the front. Support for cell phones and tablets: the holder has two kinds of connection methods, simple and quick to assemble, compatible with most cell phones and tablets. Smart app: you can download the "Pencil Sketch" app or other related software on your phone or tablet, select your favorite photo and convert it into a drawing, then start painting. The lens is made of high quality PC material, which has good toughness and is hard to break. You don't need to print pictures, it's eco-friendly and energy-saving. This tracking kit helps develop hand-eye coordination and basic drawing skills without causing eye damage.