Not only must the art be searched within which the invention claimed is classifiable, but also all analogous arts must be searched regardless of where the claimed invention is classified.
The determination of what arts are analogous to a particular claimed invention is at times difficult. It depends upon the necessary essential function or utility of the subject matter covered by the claims, and not upon what it is called by the applicant.
For example, for search purposes, a tea mixer and a concrete mixer may both be regarded as relating to the mixing art, this being the necessary function of each. Similarly a brick-cutting machine and a biscuit cutting machine may be considered as having the same necessary function. See MPEP § 2141.01(a) for a discussion of analogous and nonanalogous art in the context of establishing a prima facie case of obviousness under 35 U.S.C. 103. See MPEP § 2131.05 for a discussion of analogous and nonanalogous art in the context of 35 U.S.C. 102.