You have to read the verticals downwards: 3 = x - 3. There's a note about it in the "↓01" button. Otherwise things like 8 - x = 9 - y vertically would be ambi

You have to read the verticals downwards: 3 = x - 3. There's a note about it in the "↓01" button. Otherwise things like 8 - x = 9 - y vertically would be ambiguous.