>
Its actually the center of the buttonUpvoted for putting in the effort, and because you make a correct point.
But the Unicode button is perceptually off center, because ASCII is a smaller word, and there's no visible boundary between the buttons. This comes up a lot in iconography, the classic example is a play triangle (like the media control) in a circle. Placing the triangle in the geometric center won't look centered, it needs to be a tiny bit to the right of that to account for the shape.
No separation between the buttons means you can't see the bounds which the words are centered in, so it looks off.
The 8 and 10 have the same problem, for the same reason. A visible background-gray line between the buttons would solve this problem, it should be 'squircled' to make it I-shaped and match the outer edges.