The requirement of Art. 123(2) EPC as applied to the claims means that it is only permissible to delete features from an independent claim if there is a clear and unambiguous basis for a claim lacking these features in the application as originally filed (T 1726/06, referring to T 66/85, OJ 1989, 167).
The board in T 755/12 pointed out that, although some tests such as the essentiality test (see in this chapter II.E.1.4.3 and 1.4.4 below) have been used as an aid in assessing the allowability of amendments, they could not replace the need to answer the question of what a skilled person would objectively have derived from the description, claims and drawings of a European patent application on the date of filing (G 3/89, OJ 1993, 117, see in this chapter II.E.1.3.1 "Gold standard: directly and unambiguously derivable" above). For further decisions highlighting that these tests are only tools and do not take the place of the "gold standard", see T 648/10 and the decisions cited in this chapter II.E.1.4.4 b).
The board in T 2599/12, after finding that that the amendment complied with the "gold standard", held that there was no need for any further investigation, such as applying the test laid out in T 331/87 (see in this chapter II.E.1.4.4 "The essentiality or three-point test" below). Ultimately, this test was meant to provide an indication of whether an amendment complied with Art. 123(2) EPC as interpreted according to the "gold standard". It did not take the place of the "gold standard" and should not lead to a different result than when applying the "gold standard" directly.
In T 558/13 claim 1 according to the main request differed from claim 1 of the earlier application as filed in that the following feature had been omitted: "... a plurality of power sources are independently provided for each of the plurality of groups." Instead, claim 1 of the main request specified that the read out circuit comprised a plurality of sample and hold circuits. The board considered that the concept of the invention as consistently presented in the earlier application as filed required the provision of independent power sources. It accepted the appellant's argument that the shifted timing of the reset and sample and hold circuits provided the new technical advantage of "reducing a line noise caused by an external noise". Nevertheless, in the board's view, it was not sufficient to prove that the omitted feature was "not indispensable for achieving the effect of reducing line noise caused by external noise". Such reasoning did not take sufficient account of the information conveyed by the earlier application as a whole, which was primarily concerned with providing independent power sources and which only presented the additional technical effect caused by the shifted timing as a side issue. There was no room for speculation as to which features of the disclosed invention(s) might be omitted on further reflection, if there was no explicit or implicit disclosure of the generalised subject-matter remaining after the omission of these features.