EQUATIONS IN MY BOM?

Hello

I'm trying to add a column in my bom that will add two other columns together.  When I create a new column I'm selecting the column type as an "equation".  I then click on the equation icon and select "colum 1" "+" "colum 2" from my custom properties.  When I hit enter every value is "0".  Does anyone know why all my values are "zero"?

Thanks,

Paul

SolidworksBill Of Materials