how create a multi-http graph?

Hi all,
i need to create a http response time graph for multiple hosts.
I have added in graphs.cfg this section:

[http-multi]
         TITLE Multi-host HTTP Response Times
         FNPATTERN  tcp.http.(.+).rrd
         YAXIS Seconds
         DEF:p at RRDIDX@=@RRDFN@:sec:AVERAGE
         LINE2:p at RRDIDX@#@COLOR@:@RRDPARAM@
         GPRINT:p at RRDIDX@:LAST: \: %5.1lf%s (cur)
         GPRINT:p at RRDIDX@:MAX: \: %5.1lf%s (max)
         GPRINT:p at RRDIDX@:MIN: \: %5.1lf%s (min)
         GPRINT:p at RRDIDX@:AVERAGE: \: %5.1lf%s (avg)\n

and i have used this url (work for multi-la):

https://xymon.server/xymon-cgi/showgraph.sh?host=server1,server2&color=green&service=tcp:http&graph_height=120&graph_width=576&nostale&action=view&graph=hourly 


but don't work.

Any suggestions?

thanks
Marco