In re Klein
United States Court of Appeals for the Federal Circuit
647 F.3d 1343 (2011)
Arnold Klein (plaintiff) applied for a patent on a nectar-preparation device with an adjustable divider creating two variable-sized compartments for sugar and water, removable to let the ingredients mix; the patent examiner rejected the application as obvious over prior patents for drawer organizers with movable dividers (Roberts, O'Connor, Kirkman) and prior patents for containers with fixed, non-adjustable dividers separating liquids like plasma and water for mixing (Greenspan, De Santo). The Board of Patent Appeals and Interferences affirmed, finding a skilled person would have reason to combine these references with known sugar-water ratios; Klein appealed, arguing the references weren't analogous art.
Whether prior art references from different technical fields are analogous art for an obviousness determination when the inventor facing the specific problem at hand would have had no natural reason to consider them.