monitor the progress of dd

I have to use Helix to clone a hard disk by dd. As usual, the format is:

#dd if=/dev/hda of=/dev/hdc

However, no progress can be monitored.

I open another terminal window and by means of top, I find the PID of dd. Next,

#kill -SIGUSR1 pid

Now switching back to the terminal that is running dd, the progress of how many bytes have been written on the destination drive is disclosed.