Thanks for writing.
This feature is called load on demand and currently the chart does not support it out of the box. Since the chart does not expose events at the moment, you can create a dependency property and bind it to the chart's Pan property. This way you will be able to listen to property changes and when the property value gets to the maximum pan you can load more data.
I agree that's not the most convenient way but it should do the trick. We will see what we can do to improve the chart API for a future release.
Please write again if you need further assistance.
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