Look at it another way, if you've done the same calculations...

Look at it another way, if you've done the same calculations yesterday, today and tomorrow will you get the same value?
No, because the basis of your calculation is the current price, which is fluctuating - whilst everything else in your calculations remains the same. The question for me is how much has the current SP taken into account "the impact that IO, Oil and Copper " already?
So that is why I'm suggesting that if you are going to do this sort of calculation than pick a fixed SP starting price - however, which starting price is up to you