There are many efforts underway to unify the principle of equivalence.
For example, in Article 21, paragraph 2, of the "Basic Recommendations" promulgated by the World Intellectual Property Organization in 1991 to supplement the Paris Convention, it reads:
"(a) (.. .) The claim shall not only cover the elements present in the claim, but shall also include equivalent elements ("equivalent elements"), if the claim is infringed upon. For an invention in a claim that satisfies any of the following conditions, it should generally be considered as an equivalent of an element in the claim:
(i) The equivalent element performs in essentially the same way and is essentially the same function and produce essentially the same result, or
(ii) it is obvious to a person skilled in the art that the same effect as the element expressed in the claim can be achieved by using equivalent elements ."
In the "European Patent Convention 2000 Amendment" (referred to as "EPC2000") that came into effect on December 13, 2007, it includes rules for interpreting claims in different member states. A revised version of the "Agreement on the Interpretation of Article 69 of the European Patent Convention" that raises uniformity to the national level. The revised text reads:
In order to determine the scope of protection of a European patent, any elements equivalent to the elements stated in the claim should be taken into account.
However, there is no definition of "equivalent" in the Agreement. It is therefore also expected that this missing definition will not contribute to achieving the desired unified interpretation.