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The data points included in the second chart are those with percentages less than the specified percentage. The percentage only takes effect if the chart's BopPopSplitType is set to Percent.

This defaults to 10 when creating a new Bar of Pie or Pie of Pie series (although the type defaults to Position, so it won't have any affect).
If this is set to a value less than 0, it will be set to 0.
If this is set to a value greater than 100, it will be set to 100.

If UseDefaultSplitValue is set to true, the value of this is undefined. Setting this will set UseDefaultSplitValue to false.

For series that are not Bar Of Pie or Pie of Pie series, setting this will have no effect and it will always return 0.