I tried adding that in the function setdisplay, underneath $ca->configure(-type => $typ); but it didnt' work. The console behind my graph, prints the message

ERROR in Tk::Graph:Tk::Graph::set #947: Option '-type' is incorrect! (
+) at /home/others/it/itwi/perl/lib/perl5/site_perl/5.6.1/Tk/Graph.pm 
+line 1802, <IN> line 9318.
Bars
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The last line which says'Bars' is the contents of the $typ variable being passed to the setdisplay function. Which whould be correct, I don't know why it is reporting -type is incorrect?