Can the result of a parent item be used as the input value of a child item?

I was trying to make an item a child of another item, and then feed the result into the child item, like in this example, the parent item does a bunch of math to get the tonnage of rebar. The child item, tie wire, only needs to know the tonnage so it can determine accessory items as a factor of the tonnage.

Can the result of the parent be fed into the child? Maybe through something like [../Result]. That way it would always just look to the parent and pull the end number.