What is the test for apportioning patent profits between a plaintiff and a defendant?

The result of the requirement of a causal link between the infringement and the defendant’s profits is that the referee may have to apportion those profits between those that were caused by the infringement and those that were not. The former rightfully belong to the plaintiff, while the latter do not. The authorities are clear that it is the defendant who has the onus of establishing that a portion of its profits was not made as a result of the infringement. Rouleau J., on a reference in Beloit v. Valmet Oy, supra, at p. 457, stated the proposition in the following way: The onus is on the defendant to adduce sufficient evidence to satisfy the court that consumer demand for its product arose by virtue of features other than the plaintiffs’ infringed patent. If the defendant’s evidence in this regard is inadequate, the court will not make an apportionment.