Draw the multiple points on same label

I have one problem for gruff. I am able to create the graph by using the
gruff lib.

I have written the following code for this:-
g = Gruff::Line.new(600)

g.data("Round", [60, 50, 30, 40, 54, 31,75,45,50,54], '#DF0101')
g.labels = {0 => '2009-12-30',1=>'2009-12-29'}
send_data(g.to_blob, :disposition => 'inline', :type => 'image/png',

:filename => “arbitaryfilename.png”)

My problem is I have multiple values for single x-axis label.
How should I do that?

Can anyone help me out?