Although the standard of proof is the same for all objections covered by Art. 100 EPC (cf. T 270/90, OJ 1993, 725), the case law identifies two levels or standards of proof to be applied with regard to disputes around public prior use – either the "balance of probabilities" or "up to the hilt".
Even though different concepts as to the standard of proof have developed in the case law of the boards, they all have in common that a judgement is to be made on the basis of the application of the principle of free evaluation of evidence.