You might use a formula to keep track of it.
Rather than one or two line posts, try posting example data and the expected output.
You state that you want @ProductLine', but not for what purpose, so if I did work this out for you, it still might not satisfy your requirements because you haven't posted them.
What do you need to do, and where?
Do you want the value of @ProductLine', or to display @ProductLine', or use it to determine something else?
-k