 Yeah, so when you look at a lit device or you look at anything up close, the way your eye works is the internal muscles have to focus, kind of like focusing a camera. And the closer something is to you, the more the muscle has to tense up or tighten so that you can see properly. And that's normal. But if you spend all day looking at device and switching from one to the next, well, the muscles can get tired. And your brain is going to cope with that. And many times what it does in children, it says, well,