What is the clock on?
The clock is on the tower.
   src        edge_attr  dst
0    0  to the right of    6
1    0  to the right of    5
2    1               on    0
3    4  to the right of    6
4    5               on    6
5    5   to the left of    0
6    6   to the left of    4
7    6   to the left of    0
8    6   to the left of    9
9    9  to the right of    6