validation help required

[eluser]Computerzworld[/eluser]
Here is the callback function which i have used to compare two combobox's value....

Code:

function stationCheck($str)
    {
        if ($this->input->post("startStation")==$this->input->post("endStation"))
        {
            $this->validation->set_message('stationCheck', 'Start station and end station can not be same');
            return FALSE;
        }
        else
        {
            return TRUE;
        }
    }