Pivot table Weighted average not the sum of its parts - why?

[5h1v]

I have a pivot table that is working out weighted average, now my issue is that the Grand total does tie back to the line by line version, any idea why?

The Grand total is saying 78.56% but if I calculate it line by line its 78.14% what is causing the difference?

[TABLE="width: 673"]
<colgroup><col><col><col><col><col></colgroup><tbody>[TR]
[TD]Item[/TD]
[TD]Weighted Avg[/TD]
[TD]Qty[/TD]
[TD]Weighting[/TD]
[TD]WTD[/TD]
[/TR]
[TR]
[TD]A[/TD]
[TD]68.86%[/TD]
[TD] 82,275.00[/TD]
[TD]2.42%[/TD]
[TD]1.67%[/TD]
[/TR]
[TR]
[TD]B[/TD]
[TD]75.24%[/TD]
[TD] 411,112.50[/TD]
[TD]12.09%[/TD]
[TD]9.09%[/TD]
[/TR]
[TR]
[TD]C[/TD]
[TD]77.65%[/TD]
[TD] 97,500.00[/TD]
[TD]2.87%[/TD]
[TD]2.23%[/TD]
[/TR]
[TR]
[TD]D[/TD]
[TD]57.99%[/TD]
[TD] 3,150.00[/TD]
[TD]0.09%[/TD]
[TD]0.05%[/TD]
[/TR]
[TR]
[TD]E[/TD]
[TD]80.60%[/TD]
[TD] 1,701,300.00[/TD]
[TD]50.01%[/TD]
[TD]40.31%[/TD]
[/TR]
[TR]
[TD]F[/TD]
[TD]71.49%[/TD]
[TD] 56,150.00[/TD]
[TD]1.65%[/TD]
[TD]1.18%[/TD]
[/TR]
[TR]
[TD]G[/TD]
[TD]78.23%[/TD]
[TD] 7,950.00[/TD]
[TD]0.23%[/TD]
[TD]0.18%[/TD]
[/TR]
[TR]
[TD]H[/TD]
[TD]72.34%[/TD]
[TD] 104,625.00[/TD]
[TD]3.08%[/TD]
[TD]2.22%[/TD]
[/TR]
[TR]
[TD]I[/TD]
[TD]79.22%[/TD]
[TD] 208,975.00[/TD]
[TD]6.14%[/TD]
[TD]4.87%[/TD]
[/TR]
[TR]
[TD]J[/TD]
[TD]76.53%[/TD]
[TD] 435,487.50[/TD]
[TD]12.80%[/TD]
[TD]9.80%[/TD]
[/TR]
[TR]
[TD]K[/TD]
[TD]77.77%[/TD]
[TD] 90,875.00[/TD]
[TD]2.67%[/TD]
[TD]2.08%[/TD]
[/TR]
[TR]
[TD]L[/TD]
[TD]70.85%[/TD]
[TD] 29,400.00[/TD]
[TD]0.86%[/TD]
[TD]0.61%[/TD]
[/TR]
[TR]
[TD]M[/TD]
[TD]76.16%[/TD]
[TD] 165,300.00[/TD]
[TD]4.86%[/TD]
[TD]3.70%[/TD]
[/TR]
[TR]
[TD]N[/TD]
[TD]67.99%[/TD]
[TD] 7,525.00[/TD]
[TD]0.22%[/TD]
[TD]0.15%[/TD]
[/TR]
[TR]
[TD]Grand Total[/TD]
[TD]78.56%[/TD]
[TD] 3,401,625.00[/TD]
[TD][/TD]
[TD]78.14%


[/TD]
[/TR]
</tbody>[/TABLE]


I hope that makes sense,

Cheers for the help.

 

[pbornemeier]

Figuring the distribution of the Quantity column over its total does result in the values in the Weighting column.
How is your PT data laid out?
Which of those columns are in each PT Field (column, row, value)
What does WTD stand for?