The legal test is whether the allegedly infringing device performs "substantially the same function in substantially the same way to obtain the same result." See, e.g., Malta v. Schulmerich Carillons, Inc. 952 F.2d 1320, 1327 (Fed. Cir. 1991). How easy is it for a court to determine this?
As far back in 1818, Justice Story on the U.S. Supreme Court commented that:
"In all my experience I can scarcely recollect a single instance, in which the general question, whether the principles of two machines were the same or different, has not produced from different witnesses, equally credible and equally intelligent, opposite answers." Barrett v. Hall, 2 F. Cas. 914, 923 (C.C.D. Mass. 1818).
As far back in 1818, Justice Story on the U.S. Supreme Court commented that:
"In all my experience I can scarcely recollect a single instance, in which the general question, whether the principles of two machines were the same or different, has not produced from different witnesses, equally credible and equally intelligent, opposite answers." Barrett v. Hall, 2 F. Cas. 914, 923 (C.C.D. Mass. 1818).