Once a second, the network interfaces are queried for the amount of
data that was exchanged. The data from the selected interface is drawn
in the graph. As data is sampled, the scale of the graph will change
and is set to the maximum value seen in the data "window". The value
of the maximum data rate (in bytes per second) is displayed in the
lower left corner. A K or M is appended to the data rate for kilobytes
or megabytes, respectively.

You can cycle through the configured network interfaces by clicking
the mouse on the interface name. There is also a command line option
to specify which interface should be displayed first.