Read two dots together

One black dot asks for a double or a half. Here two black dots meet at the same cell, so we need to read them together. Suppose the middle cell were one. Each dot would need a two at its other end. But these two ends share a box, and a box cannot repeat two. So the centre cannot be one. Eight has the same trouble. Both dots would demand a four, repeated in the box. And a centre of three or six would also force matching outer digits. Two can take one and four as different partners. Four can take two and eight. Both arrangements respect the box, so the centre is two or four. Each dot worked alone. Reading both dots with the box rule removed four more digits from their shared cell.