What are the letters on?
The letters are on the clock.
    src        edge_attr  dst
0     0   to the left of    5
1     0   to the left of   15
2     1   to the left of   13
3     1   to the left of    7
4     1   to the left of   14
..  ...              ...  ...
62   15  to the right of   13
63   16  to the right of   10
64   16  to the right of    9
65   16  to the right of    6
66   17  to the right of   11

[67 rows x 3 columns]