U.S. Supreme Court
Garretson v. Clark, 111 U.S. 120 (1884)
Garretson v. Clark
Argued January 15, 1884
Decided March 24, 1884
111 U.S. 120
When a patent is for an improvement of an existing machine or contrivance, the patentee in a suit for damages for infringement must either show by reliable, tangible proof that the value of the machine or contrivance as a whole is due to the use of his patented invention or he must separate and apportion, by proof of the same character, the part of the defendant's profits which are derivable from the use of it in order to establish a claim for more than nominal damages.
This was a suit in equity for infringement of a patent for an improved mop head. The sole question raised was whether the evidence of damages warranted a judgment for more than nominal damages.