Now I see what is happening! :D

You are taking the percentage from the column corresponding with the drop down.
So if the machining has 0 all the way down, it appears to do nothing as 10% of 0 is 0.

This is a percentage of the "Contract Price", and the 10% being added on, needs to be pasted into the column relating to the drop down.

I hope that makes sense!

Thanks! Nick