the calculation is based on the value being passed by the size and quantity list.
it is looking at those values and using them to determine whether the calculation should be applied or not.
right now, they are not product specific, they are size and quantity specific.
if you look closesly, hey all ask a question:
abs(([Size] == '50ml') && [Quantity] < 12))?
this will evaluate to true if the size passed is 50ml and the quantity passed is less than 12.
if you wanted to make this apply to a particular product, you would need to edit the question and include the ID
abs(([ID] == "1" && [Size] == '50ml') && [Quantity] < 12))?
this would evaluate to true if the ID is 1, the size is 50ml and the quantity is less than 12.