The information to be provided pursuant to Articles 3 and 4 shall be obtained by reliable, accurate and reproducible measurement and calculation methods, which take into account the recognised state-of-the-art measurement and calculation methods, as set out in Annex IV.
Article 6
Verification procedure for market surveillance purposes
Member States shall apply the verification procedure laid down in Annex IX when performing the market surveillance checks referred to in Article 8(3) of Regulation (EU) 2017/1369.
the actual legislation is not that specific as far as i can tell:
https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX%3A32023R1669#anx_I