Perhaps a Pivot Table is the better way to go.

Data>Pivot Table
Use Excel
Select your data
Click the [Layout] button

ROW: Drag the Sector field here
DATA: Drag the Weight field here
If it doesn't list as Sum of Weight...dbl-click it and set it to Sum
Click [OK]
Select where you want the Pivot Table...and you're done!

That will list each Sector and the Total of the Weights.

To refresh the Pivot Table, just right click it and select Refresh Data

Is that something you can work with?

Regards,
Ron