As a result of the curtailment of the ‘entire market value rule‘ courts in US patent cases where infringement is found, are increasingly required to seek to apportion a proportion of the profits from sales of a product embodying an infringing feature to the infringing feature, i.e., how much of the selling price reflects that feature, how much does it cost to add, and so what margin can be attributed to it. This can and has proven to be a complex task.