Applying G 1/24 to Mathematical Methods: T 2043/23 on Explanatory Claim Interpretation
In T 2043/23, the Board of Appeal applied G 1/24 to confirm that the description may serve an explanatory function to help the skilled reader recognise an embodiment already encompassed by the claim wording.
The Enlarged Board of Appeal's mandate to consult the description for claim interpretation permits an explanatory and confirmatory function that helps the skilled reader recognise an embodiment already encompassed by the claim wording, provided it does not alter the claim's scope.
How did the description expand the mathematical scope of the resistance comparison?
In T 2043/23, the patent proprietor sought to defend EP 3 273 809, which relates to an electrically operated aerosol generating system. The central dispute concerned features 1.8 and 1.8a of the main request. These features required the electric circuitry to determine an adverse condition when a ratio between the measured initial electrical resistance of the heater and a change in electrical resistance is greater than a maximum threshold value stored in the memory.
The opposition division interpreted this wording in light of paragraph [17] of the patent. This paragraph explained that the circuitry might not actually calculate the ratio, but could instead make an equivalent direct comparison between a measured electrical resistance and a value calculated from the initial electrical resistance and a stored threshold. The patent proprietor argued that the claim clearly defined a ratio-based comparison and required no interpretation. Applying G 1/24, the Board agreed with the opposition division. The panel found that the claim merely specified the condition to be detected and left open the mathematical method of doing so.
Why does this interpretation comply with G 1/24 without improperly broadening the claim?
The Board explicitly addressed the boundaries of claim interpretation by distinguishing the present facts from T 439/22 . In that earlier decision, the description and drawings were relied upon to broaden the scope of a claim beyond what was conveyed by the claim wording read in isolation.
In the present case, the Board found that the description served an explanatory and confirmatory function (reasons 2.10). It assisted the skilled reader in recognising that the direct comparison was an embodiment already encompassed by the claim wording, without altering the scope of the claim itself. Citing T 2027/23, the panel confirmed that this modest explanatory use of the description is consistent with the principles set out by the Enlarged Board of Appeal.
Why did the direct comparison render the main request obvious over D14?
With the claim interpreted to cover the direct comparison, the Board assessed inventive step starting from document D14. This prior art disclosed an electronic cigarette that measures the heating coil's resistance at room temperature and provided a formula relating temperature to resistance.
The Board defined the objective technical problem as how to determine the maximum resistance value corresponding to the maximum permissible temperature for a particular heating element, while taking into account manufacturing variations. The panel held that the skilled person, aware of manufacturing tolerances, would obviously use the measured initial resistance in the provided formula to accurately determine the maximum resistance for that specific heating element. Consequently, the main request lacked an inventive step.
How did the expected time period feature save the first auxiliary request?
The proprietor successfully defended the patent on the basis of the first auxiliary request. This request required the circuitry to determine an adverse condition when the ratio reaches a threshold value stored in the memory outside of an expected time period.
The opponent argued that this feature was obvious over D14 combined with D4, which taught monitoring the rate of change of temperature. The opponent contended that the skilled person would obviously monitor the rate of change of resistance and measure the time taken to reach the maximum resistance. The Board rejected this hindsight reasoning. The panel concluded that while the skilled person might replace a direct comparison with an evaluation of the rate of change of resistance, they would have no reason to introduce the specific notion of an expected time period and determine whether the measured resistance reaches the maximum outside of that period (reasons 4.8).
What should practitioners consider when relying on the description after T 2043/23?
This decision illustrates a practical boundary for the application of G 1/24. When arguing for a specific interpretation of a claim feature based on the description, parties should demonstrate that the description serves an explanatory and confirmatory function for an embodiment already encompassed by the claim language. If the description is used to stretch the claim scope beyond what the wording itself can convey, the interpretation is likely to fail. Furthermore, when attacking inventive step based on a combination of documents, opponents should ensure their chain of reasoning leads to the claimed mechanism. As shown here, arguing that a prior art concept like rate of change is equivalent to a specific temporal threshold evaluation is unlikely to suffice without a pointer in the prior art.
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