Im trying to write a methodology of a website and is considering to use black box testing and writing cases for it. But i saw a research paper using black box testing and just measuring it by scale 1 by lowest 5 by highest. Im wondering how they measured its functionality by a scale

Heres a link to the research paper

http://irjaes.com/wp-content/uploads/2022/04/IRJAES-V7N2P71Y22.pdf