With the current implementation the top level header only visually appears as one cell, however it stretches the subheader column below (check PivotGrid(Now).png).


Looking the attach file,now the XAML is following:
<pivot:LocalDataSourceProvider.AggregateDescriptions>
                        <pivot:PropertyAggregateDescription PropertyName="AccValue" CustomName="total"/>
                        <pivot:PropertyAggregateDescription PropertyName="IncValue" CustomName="increased"/>
                 </pivot:LocalDataSourceProvider.AggregateDescriptions>

 <pivot:LocalDataSourceProvider.ColumnGroupDescriptions>
                        <pivot:PropertyGroupDescription PropertyName="SystemDeviceCode"/>
                    </pivot:LocalDataSourceProvider.ColumnGroupDescriptions>
the SystemDeviceCode column just use one column ,like the attach "PivotGrid(Now).png",when the text is long ,the first column "Total" is too wide .
I hope like the attach "PivotGrid(desired).PNG",the SystemDeviceCode column can span two columns.
     and the data struct:

 public class DayStruct1
    {
        public string HourNum { get; set; }
        public string SystemDeviceCode { get; set; }
        public double AccValue { get; set; }
        public double IncValue { get; set; }
        public DateTime Date { get; set; }
    }//