Roll up Lookups With Negative number


I have a column of lookup to return relation of a tables containing number, (Hopefully 1 positive and 1 negative to indicated the status of the item.

i tried to rollup the relation, however sum is not available.

i then tried to rollup the lookup field, it is not selectable in the drop down.

Below f

You can try using a math column, point to your If Then Else and multiply by one, then try rolling that up instead of the original one.