I'm sorry, that property do not limit the number of results displayed per page. More explicitly, the property charting.data.count represent The number of results to retrieve from events. Set to 0, to get all results and default to 1000. You can decide to retrieve 1000 results from events, and display only 20 with limit, head, .... commands
For more informations concernin charting options, start here: http://docs.splunk.com/Documentation/Splunk/6.0.1/Viz/ChartConfigurationReference
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