Bull's-eye principle _ What does bull's-eye mean?

In shooting competition, athletes should close one eye, and then the other eye is in line with the bull's-eye on the gun. What principle is used?

Nothing like it. Target. But according to the door beacon. The physical principle used is that two points determine a straight line. Think about it: the right eye sees the sight through the door, and the sight is aimed at the target. Here you can see two straight lines: the door leading to the sight and the sight leading to the target. According to the fact that the door and the sight are in a straight line and the sight and the target are in a straight line, then the door and the target are in a straight line. The barrel and the target are in a straight line.

I hope you can understand!