Crystal Report Charts

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Hi, I have a problem drawing charts in crystal reports.
I have a dataset from an xml file which contains the following information
as an example:

<DocumentElement>
<CarParkHistory>
<Count>111</Count>
<DateTime>27/09/2008 00:00:00</DateTime>
<Location>Location A</Location>
</CarParkHistory>
<CarParkHistory>
<Count>253</Count>
<DateTime>27/09/2008 00:00:00</DateTime>
<Location>Location B</Location>
</CarParkHistory>
<CarParkHistory>
<Count>593</Count>
<DateTime>27/09/2008 00:00:00</DateTime>
<Location>Location C</Location>
</CarParkHistory>
<CarParkHistory>
<Count>519</Count>
<DateTime>27/09/2008 00:15:00</DateTime>
<Location>Location A</Location>
</CarParkHistory>
<CarParkHistory>
<Count>21</Count>
<DateTime>27/09/2008 00:15:00</DateTime>
<Location>Location B</Location>
</CarParkHistory>
<CarParkHistory>
<Count>296</Count>
<DateTime>27/09/2008 00:15:00</DateTime>
<Location>Location C</Location>
</CarParkHistory>
:
:
</DocumentElement>

What I need to be able to do is plot a chart for every DateTime the count
for each location. So in the above example I would like 3 lines on a graph
each showing the counts for the individual car parks.
Can someone explain how to do this please?